3 with a 6 speed.
2 with a 5 speed.
if using the common 4.1 & 4.3:1 final drives
Rich.
If you had sufficient power with a very wide flat torque band, the five speed might actually be quicker because of one less shift.
How about a clutched auto ?
Use the clutch only to start off in first gear from standstill.
Keep full throttle and allow the auto to shift up or down through the gears, no torque converter required.
If you use an electronic auto, you can not only map all the shift points versus throttle opening, but also how hard it shifts.
You might not want the tires to chirp during every shift, you can set it to shift as hard or softly as you want, because the control solenoids are all pwm'd.
Even run different programs for track/road.
How about a very common garden variety electronic 4L60E with aftermarket programmable controller, and a good strong Miata clutch ?
Factory rated 350 ft/Lb for five litre engine and there are much heavier duty suv and truck versions that go way higher.
I believe the Miata six speed is rated 120 Ft/Lb not sure.
They are not that large either. The bell housing and torque converter are huge, but we don't need them. The actual guts of the transmission are no larger than a manual box. I have one here in fact to look at.
1st 3.059 say 50Kmh at 7,000
2nd 1.625 98Kmh at 7,000
3rd 1.00 161 Kmh at 7,000
4th 0.696 230 Kmh at 7,000 (about 3,181 at 100 Kmh).
The only down side is you drop a lot of rpm during changes.
1st to 2nd, rpm drops to 3,178.
2nd to 3rd, rpm drops to 4,307.
3rd to 4th, rpm drops to 4,872.
With forced induction particularly with a turbo, full throttle gear shifts will maintain boost during the shift.
If its fully spooled at 3,000 and right up on the torque curve above that, you don't need closer ratios.
Definitely not suitable for a highly tuned normally aspirated engine, but with forced induction say 300Hp+ It might go pretty well on the road and be very easy to drive.
Just one more of my random what if thoughts....................