bassetts on an e30....fitment/backspacing question

[worangejuice]

195/50or45/15

[z31maniac]

what tire size you plan to run?

[worangejuice]

Sup guys.........
What measurement of backspacing should I get for my E30?
looking at bassetts in 15x8

http://www.bassettwheel.com/legends_mini.html

Ive been looking at this, but not sure if its 1000% correct

So gauging off this I should get 4" and 4.75 backspacing.
The e30 sits prety flush on +20, but I dont mind a little poke or whatevs. Gonna get a fender roll to compensate as well, lowered on springs.
heres how she sits right now.


So just need good reccommendations on the backspacing I need to order.
Thanks guys!!!