Consensus on 15x7? 15x8?

[royalblue325]

So I think I want to buy some Kosei K8Rs ( http://www.tirerack.com/wheels/Wheel...kageFlow=false )
or Kosei K1s.

The K8Rs are 15x8, whereas the K1s are 15x7. What is the general knowledge on which is better? I know if you run 225/50/15s you might have some rub, but the K8Rs are 20 offset, which I think is the perfect e30 offset. I'm sorry for being ignorant, but I'm new to cars and my wheel knowledge is lacking. Thanks for any help that I can get!
(PS, I have an 88 325i that I will be mostly using for street use, but will have some autocrosses and track events for also. I want the car to be as fast as possible. Thank you)

[ak-]

There was some test done on a 7" wide vs an 8" wide where no matter what, a bigger tire didn't result in more grip for the 7" wheel until they placed the tire on the 8" wide wheel which resulted in faster lap times.

You'll have to roll your rear fenders for the 225 on et20 I believe.