Acording to the numbers I've seen the 280ZX is the quickest Z besides the 300ZXTT. The NA 300ZX isnt far behind the turbo 280ZX so it should be a pretty good race. I guess If both your cars are tuned properly it will come down to who the better driver is.
Well, I own 4 z cars. One is a 300zx n/a, a 300zx twin turbo and a 280zxt and 280zx na. My 300zx twinturbo is the quickest, but not by much. the 280zxt is actually close maybe a 1 second off 0-60. wich I added a intercooler to it and put the boost to 12 pounds and it is faster then my 300zx twinturbo stock !! as far as stock goes 300zx n/a vs. 280zxt, the 280 is going to smoke it, I have a nice 300zx (it's the wife's) but it is bone stock and runs great but would never beet my 280zxt. and if you arent at sea level the turbo will be even better. Both are great cars but Id have to say the 280zxt is going to win. they were the best z until the twin turbo plain and simple. well have fun with your z's zzzz ya later