which of these two should i buy, both single turbo, and they can be newer or older models, but which one owuld be smarter to buy, and is faster.

what year are you looking for? if you want a single turbo i know for a fact with the 300zx you have to get the first gen. but i dont know bout the rx-7. the smarter to buy would most likely be the 300zx just because of the rotary in the rx-7. if you cant work on one yourself, then good luck. the rx-7 is faster than the 300zx in both the first and second gen. but imo, the 300zx is the better car.

an RX7 will still never be a Z.