The choice of car to use is all very complicated as it depends on if you are playing Outrun 2006 Coast 2 Coast (hereafter referred to as just Outrun 2006) or Outrun 2SP,

• Outrun 2006 is based on 2SP but should be treated as a different game.
• Outrun 2SP is the full arcade game within the game Outrun 2006.

So I will offer a full breakdown of each "Game" as Outrun 2006 is not equal to Outrun 2SP. This is why I feel the leaderboards need an overhaul:

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Outrun 2SP:
So for 2SP, you have just one "grade" of car (in Outrun or Heart Attack mode) and the top speed (without slipstreaming) is 293 Km/h. Handling is pretty much the same for all cars and really, your choice of car is aesthetic mostly.

There are two "grades" of car in Time attack mode - Normal and Tuned. Normal cars behave the same as in Heart Attack and Outrun mode (same handling & top speed). The Tuned cars offer a top speed of 300 Km/h for ALL cars and handle the same as the F40 does in Outrun 2. They also do not drop speed as you move your car left and right (Move, not turn/drift)

As mentioned, in Outrun 2SP, car choice is mostly aesthetic. Some cars may 'feel' like they behave differently (obviously with 6T vs 5T) but in general, are virtually the same and this ensured an even playing field for the arcade leaderboards at the time (Not to mention the XBL leaderboards which are long gone of course).

Please also note that there is now a dedicated game on speedrun.com for Outrun 2SP which would be friendlier to runs from this mode in Outrun 2006:
https://www.speedrun.com/outrun2sp

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Outrun 2006:
This is where things get complicated and don't go relying on the in game "stats" in the car select screen either as they are wrong.

There are two car "types" (Standard and OR) and four grades (Novice, Intermediate A, Intermediate B and Professional) for each. This applies to all game modes in C2C (Outrun, Heart Attack, Time Attack).

'Standard' cars behave similar to Outrun 2 (That's Outrun 2 - Not 2SP) in terms of handling and top speed. For Novice cars, top speed is 288Km/h, Intermediate A is 293Km/h, Intermediate B is 293Km/h and Professional is 300Km/h. I saw/felt no difference in handling between Intermediate A and B despite what the stats screen says. The only difference I detected was the A cars are 6T and the B cars are 5T. Professional cars do not lose speed as they turn. All car grades handle exactly like they do in Outrun 2.

'OR' cars are similar to the standard with some differences. For Novice cars, top speed is 300Km/h, Intermediate 5T is 304Km/h, Intermediate 6T is 307Km/h and Professional is 309Km/h. Unlike standard cars, the Intermediates do have a difference of speed and handling. '6T' cars handle better, are more 'stable' and have a faster top speed however, their acceleration is poor (the slowest of any class almost). In contrast, 5T have the fastest acceleration of anything in the game but are a bit less stable than other cars and can easily fish tail. Notably, the OR cars also DO drop speed as you move your car left and right (Move, not turn/drift). Even the professional ones.

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Notes:
• The Japanese PS2 exclusive Outrun 2SP is more or less the same for all the above and is essentially just Outrun 2006: Coast 2 Coast by a different name
• It is possible Automatic cars may behave differently in the various modes. I didn't check but, if you want to be approaching the top of any leaderboard (new or existing), you will need to master MT anyway
• Outrun Online Arcade is basically just Outrun 2SP with only 10 car models, none of the OR car variants and no 2006/Coast 2 Coast modes. While it has it's own SR.C listing, you would be better off submitting runs for this version of the game in the dedicated Outrun 2SP game:
https://www.speedrun.com/outrun2sp

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I hope the above proves useful to all - both for those wondering what car to select as well as for those that I hope will update the leaderboards into different, suitable categories (similar to my suggestions in the other topic)
https://www.speedrun.com/OutRun_2006_Coast_2_Coast/thread/37vya

Add this as a guide?