I may or may not be a help at all and I'm in any way not an expert.
Anyhow, I've experimented with tons of spacers out there, as far as
what I've tried and seen personally, it depends what style you want.
Going 20mm all around is the aggressive setup having it cambered in.
Same thing with a 15mm all around, the rear requires being cambered in while
the front will stay flush by the fender.
I've done 15/20, 15/15 and 15/10. I'm on H&R springs with SPC rear camber
kit, it may not be the springs you want/have but at least gives you an idea
where the wheel will sit.
With the nismo wheels being 19 X 9.5 +40 and 19 X 10.5 +23, having 15/10
puts the offset at +25 and +13 respectively, close to the most preferred
offset of +22 and +12.
And not trying to be a smart a**, there are no spacers for now that makes
the wheel and rotor looks like there's no spacer due to I'm assuming
weight reasons. What I've done is by installing Stillen's 1pc rotor that is zinc coated
making it unnoticeable.
Now, there are a lot of factors to be considered still, with the setup I have
the wheels sit flush by the fender and I was able to rock wide tires, 265/35/19
and 305/30/19, and still stay on OEM camber settings.
Enough talk, here are some pics of mine:
A drop would finalize the look of the rear.