300ZX all the way.
300ZX TT weighes 3400 lbs and has 300HP and is a very reliable engine...wish I could say the same for the VR4..it's a reliability nightmare. You will spend so much money trying to fix it than actually making it faster. The VR4 is a brick...weighing in at 3800 lbs. It does have 320HP but the way it gets to 60 mph is slow...5.7 seconds...compared to the 300ZX getting to 60 mph in 5.2 seconds.
Here's a comparison done of the RX-7, Corvette, Porsche 968, Supra TT, 300ZX, and 3000GT VR-4...the 300ZX came in second while the 3000GT VR4 came in 6th (last place).
http://www.nutsandvolts.com/rx7/arti...article_p1.asp