Personally I have Mousewheeldown bound to reload, allowing for instant full barrel reloads without the need of the upgrade, and Mousewheelup bound to use, allowing those really rapid inputs during the sell glitch. This can take a while to get used to (especially the "use") but it's definitively worth it.

The speed at which you'll be able to sell is also bound to your framerate (as more frames = more inputs that can be registered per second; be also wary that you need to have a particular rhythm with the mousewheel, especially at 60 FPS, as going too fast will completely ignore inputs and therefore sell slower). The technique I use to fast-sell with Mousewheelup is to simply alternate scrolling with both my Index fingers, keeping the scrolling motion mostly uninterrupted.

From memory, the difference between 60 FPS and higher is only 2 or 3 seconds per 10.000$ farmed, so this is not something to think too much about unless you're aiming for very top times.

Hope this helps you ;)