In my opinion 0-60 is nothing but pure marketing, they love giving you a one shift to 60 but that's where the benefit stops. If you're only accelerating to 60 then yeah the five speeds are great. If you're going faster a six speed combined with the right rear end gets you past 60 quicker. You might be behind at 60 but by 70 you've caught back up and it's just gains beyond that and more overall time in the sweet spot of the torque curve.
That said that's considering peaks for a Miata which in stock form is hitting peak torque about 1500-2000 rpm higher than the x-wedge.
If anyone knows the ratio of the bevel box and belt pulleys some more maths could be done to see just where it would stand, and that's of course still just theory. Real world performance would eventually be the only way. That said I have friends in Miata clubs with spare transmissions and have already had this thought myself, just need my three wheeler first
