[electlatino]

having GFX and having been shopping for an exhaust for some time, let me tell you what i've learned from my experience:

exhaust first.

i've had several vendors tell me they can't do it with GFX kit already on (maybe they don't want to do it, but whatever). the GFX extends back further over the stock exhaust and makes it hard to get the stock exhaust out and the new exhaust in.

i've also had my stock exhaust replaced with another exhaust through my warranty, so it was the exact same thing. (baffler went loose in the right muffler.) dealership told me they had to "machine" the exhaust to get it to fit. now the tips don't stick out as much as the first exhaust

it's much easier to do exhaust first, then GFX kit.

if you're really worried about it not fitting, then you need to make sure you talk to the manufacturer and confirm their exhaust will fit on a GFX kit. some (SLP, for example), make one exhaust for GFX cars and one exhaust for non-GFX cars. some exhaust systems (JBA) are neutral and will fit both (i called and asked because that's what i'm getting!!!) some only fit one style and will not fit the other.

long story short, exhaust first, then GFX. call the manufacturer to verify it will in fact fit with a GFX kit before you buy it. if it won't, then you have a harder choice...get the exhaust you want and sacrifice the GFX kit, or get the GFX and sacrifice the exhaust you wanted for another.....