With those mods I'd expect you to be very low 13's if not high 12's (gears mainly) and if what you say about S2000's running high 13's to low 14's I'm very surprised it was even a race. Do you have longtubes?
I did better on the street with the 3.27's! Its a little trick to hook with 4.30's on radials in December! I was feathering th first 2 gears and when hooked I pulled several cars.
the s2k is a decent car but they are hell to launch
it is easy to either bog them or spin the tires but finding that middle ground where you hook and go is a pain
a lot of times it is with a lot of slipping of the clutch
best time I have heard of is I think a 13.87 fully stock and I can find a vid of that one if you like
but seems most pull mid 14's or so on avg
the s2k is a drivers car not very forgiving on the launch or shifting
all in all GT vs s2k would be a drivers race
cobra I have no clue I can only assume that they are a mid 13 ON AVG but I'm sure they would put the beat down on a s2k unless the driver messes up
I ran an s2000 fron a rolling (about 50mph) start 5 times in about 10 miles with my 97 cobra. I always had him by at least 2 lenghts and over 130 I was walking away from him hard. I ran the same guy a few weeks later, he was in a turbo eclipse spyder this time, it was a much closer race but I was still ahead by 1/2 a length at the least and started walking away from him at about the same point. I run into him every couple of weeks in the same spot on the highway and we always play.