There's a certain set of wheels I am looking at, the largest size is 19x9.5 and they come in et35 and et45. I have gt500 6pistons on the front. Which offset will clear them?

 

I have 285/30zr20 x 9.5et35 on the front with 4pot Brembo.

 

It depends on the wheel. The +35 will give you more clearance than the +45. I'd buy one and test the clearance, then buy the rest if you're good. I've ran 19x9.5 +35 wheels all around with the 4-piston Brembos and had plenty of clearance but they were a concave wheel. Id you're looking at a flat face wheel (like say the Bullitt style), then it's really hard to say. You'll most likely be fine because the 6-piston Brembos are actually narrower than the 4-piston calipers, but I'd still just buy one wheel to be sure.