HardcoreABN

I have the option of going with either a M6 or a M12 transmission for my C5. 402LS2, LS3 heads, should be about 525-550rwhp NA with up to 300 in nitrous on top of it. Which trans would be the better choice, as I have both. Car is a daily driver that will also see regular track time.

PewterScreaminMach

Depends on your purpose for the car and your rear gears but generally:

- Drag strip, ET goals, and/or dig runs? MN12.

- Messin around on the highway, cruisin, and don't care about going quicker at the drag strip? MN6.

Just my personal opinion after having both and using them for all of those different situations. The MN12 gets you off the line quicker with those steeper gears but has a weird dead spot between 3rd and 4th (less noticeable the higher you go in terms of power, obviously, and probably negligible at your power level with a 300 shot on top of that). From a roll, it can put you in a strange spot, especially if you're on the highway messin around from those speeds (legally, of course...). I never liked it as much on the street for cruising or....fun....but there was no denying the ET improvement at the track. On the other hand, the MN6 feels a bit more "balanced" to me for cruising and the longer gearing might give noticably better gas mileage depending on how steep your rear gearing is, especially in the overdrive gears (if you even care about that).