We are at a point in speedrunning mainly San Andreas and GTA III where sometimes you have to hold down so many keys at a time, that - if you don't have an N-key rollover keyboard (all keys can be registered at the same time) - you might encounter issues, potentially losing time in your runs or even dying / failing missions. Sometimes up to 5-6 keys have to be pressed at the same time. Not for a long period, but even if just one of these keypresses fail to register, sometimes chaos is inevitable.

It is also possible, that you didn't find the default control scheme satisfactory and changed it around a bit to suit your needs better.

I'd like to ask what kind of key and mouse button mappings have you set up for either SA or III? Also if you are using a tenkeyless keyboard, what have you remapped special controls to (hydraulics, forklift, hydra)? I feel like this mainly involves these 2 games because of holding phonecalls / submission key, so didn't want to post in GTA general forums.

My settings:
I personally found holding Tab while driving to be uncomfortable, so I switched to the key I use in III, Caps Lock as my action / alt fire key. On one of my older keyboards I couldn't hold caps lock + W + E at the same time to drive-by, so I tried remapping looking right to R, but it feelt a bit awkward. I also use MMB to raise height in plane / do a wheelie and RMB to lower / lean forward. I also use left shift for sprinting and space for jumping. In GTA III my camera change key is Num 3, which is right next to look left / right / back with Num1 and 2 and ensures my hand is close to the mouse.
On 60-80% sized keyboards I'd use the keys to the left of enter in an upside down T shape for special controls. For GTA III I move the idea on the Numpad (1-3) over to left and right square bracket and backslash (right over Enter on the ANSI layout).

My setup changed quite a bit over time: I also found tab uncomfortable, so I switched to left shift to hold calls, but I used that to jump... so I mapped jump to caps lock. Not the best, but it worked. Got a bit tired of caps lock being randomly on/off after runs + pressing it while having a call held with shift wasn't convenient, so I eventually mapped it to one of my mouse buttons instead.

I also used to use the side mouse buttons for leaning while driving bikes, but RMB was more convenient to press rapidly than the side buttons so now I lean back with the side button, but forward with RMB.

I have honking on MMB, very easy to get to for dealing with cops.

And probably the most minor one... Because of the keyboard ghosting issues, I can't hold WAS at the same time, so I mapped a secondary brake/reverse to X so I can do the 360 in driving school.

I have a Logitech g600 mouse which has a numpad on the side which I can bind anything to, so I'm not sure how useful my settings are (who wants to use "4" for holding a call?)

I've learned to manage with holding Tab, however I've mapped lean forward to Lshift, Hydra and Forklift are Numpad + and Numpad Enter. Hydraulics are Num8, Num2, Num4 and Num6.
My keyboard doesn't support N-key rollover and my mouse is default settings

LMB - lean forward
RMB - lean backwards
MXB1 (mouse side button ) - phone calls
Left shift - honking
Default hydra/hydraulics controls (numpad)

Pretty comfortable

rmb lean forward
down - lean backward
lctrl - call
h - honking
comfortable as fuck

Everything by default, except that I use alt to jump (No, I don't dupe, so I don't have to worry about alt+tab)

LCTRL - jump
TAB - taking calls
XMB1 - looking behind
XMB2 - holding calls

1/LMB - lean forward
2/XMB1 - lean backwards
RMB - honking
` - sub-mission

capslock=xmb1 because dinput

I bind phone call to side mouse button (mouse4). I find it easier to hold down than keys.
The other side mouse button for honking (mouse5) 🙂
Everything else is default other than lean forward and back on a bike with mouse1 and mouse2. Flying with arrow keys

I only run GTA 3, so I can't help with speedrunning SA, but I use:
WASD for driving/moving
Enter for camera change
LShift to sprint (and honk)
Space to jump(and handbrake)
Caps Lock to look back (on foot) and sub-mission
Q+E for looking left and right
MMB to look backward
RMB to aim and LMB to shoot
Scroll wheel to change weapons on foot (and scroll up to change radio in a car)

SAN ANDREAS
Most of the things are set on default for me. These are the only things I've changed:

Action - Middle Mouse / Extra Mouse Button (depends on whether I use DINPUT or not, extra buttons only work without it)
RMB - Leaning forward (I prefer this one because I can still despawn vehicles while driving a bike)

Other than these I use Alt for leaning forward as well and Left Shift for leaning backwards. I use this when I'm flying and holding a phone call at the same time. This isn't needed if you use something like Capslock/Shift/Ctrl as an action key.

Being on a bike is another great use of setting leaning backwards like this.

III
Default stuff again except:

Left Alt - Despawning traffic (aka changing the camera) (I don't like to take my hand off the mouse unless I'm flying the dodo)
Extra Mouse Button - Submission (It's easier to hold taxi and other submissions, especially through the mission SCaM)

Arrow up - Dodo down
Arrow down - Dodo up

I simply set this to make dodo flying at least a little similar to San Andreas (Default is Num 9 and Num 6)

WASD for moving
Shift for sprint, Space for jump (like literally every other game does it)
Shift for horn, Space for handbrake
2 for submission
Q, E & MMB for looking in directions
F for enter exit
Tab for phonecall action

B for leaning forward, N for leaning back on bike (and the equivalents for planes/helis/flying cars)
X and C for forklift/dozer/dumper controls etc (also hydra thrusters, but I use default Num 8 and Num 2 for hydra as I need my left Thumb on B + N
Numpad 4 Special Control Right
Numpad 6 Special Control Left (No, I didn't mix these up)

Fire: LMB
Alt Fire: RMB
I have these bound to keyboards keys as well, but dont recall using them in recent years.

Change camera: V
Change radio: R / mousewheel
Change UTP Song: F5

Y and N for talking and trip skipping etc

G and H for gang controls (holding H disbands the group)

Mwheel for Camera and sniper zoom

Lalt for walk, C for crouch

RMB for aim

How can i use the XMB buttons. I can't do this in GTA Settings.

You might be using the mouse fix dll. The best thing to do is binding them to keyboard keys, either via mouse software or via autohotkey

I downloaded a mousefix dll named "DINPUT8.dll" but it doesn't work. I'm using XMouse Controller but I want to do it in game settings. What can i do?

use compatipility mode:
windows 98/windows me
it worked for me
but your save directory will relocate to users/public/documents/gtasanandreas

It doesn't work.

if you have a gamepad/controller plug it in then open the game while in game unplug the controller then your mouse might work. gta sa is a glitchy game especially on new hardware