Wheelbase: 96.7"
track width (depends on tires and wheels, yours are not the same as listed on the specs page!)
spring motion ratios are around 0.96 front and rear. front swaybar motion ratio is ~0.58, rear is about 0.96.
I never did tip tests to determine Hcg, but having worked on both, I'd expect the spyder to come in at least half an inch or so below an sts miata.
things that are missing that are suspect to the validity of the model. Didn't ask for:
data on polar moment. this makes for a big difference in transients. (favors the spyder, if the driver has the skill to take advantage.)
front and rear track widths separately. This can make a big difference. Looks to favor the spyder by 2.5" from the s2k, and 1.5" from the nc. if these numbers are even close to correct, this is simply HUGE.
Bump and roll steer behavior, etc etc etc.
Tire diameter (this affects the effective drive ratio, and the 3 cars don't use the same rolling diameter, so it will make a difference). If the program doesn't ask for it, the final drive can be fudged to account for it.
Also, what are you using for redline? 6850 is the spec, but you can easily get to 7100 in 1st and 2nd in most cars.
edit: I see your new message. That not accounting for path differences due to width thing is huge. It is wrong to ignore that for autocross, thought at much larger corners/higher speeds, it isn't very important. That is probably a bigger error than the more wrong assumption that all the suspensions are equally effective in all situations. It would be nice to at least know which way the error due to ignoring width will be. The rear track width dominates, so the car that is narrowest in the rear will have an advantage not shown in the sim. Looks like the stock widths are 2.5" in favor of the spyder over the s2k and 1.5 over the NC. Not sure how that changes with race tires and camber on the s2k and NC.
another question... does the free version overlap braking, acceleration, and cornering, or segment them? this simplification isn't as bad for road racing as for autocross. this error would also undersell the spyder. Of course the tire and power assumptions really favor the s2k (as in, they should do better than the sim assumes).
Also, peak g loads from a DAQ are misleading. better to take the highest g's in any direction that is sustained for over a half second or so.