I don't have experience with the xFire, but I run a wide setup on my F-Body. My setup used a wider offset, and my tires don't tuck inside the fender. This minimized my rubbing on the inner wheel wells. I was advised to roll the inner lip a little bit, otherwise the metal could cut my tire tread, but I tested before taking this route, just trying to drive aggressively and see if I was rubbing paint off the fender or cutting my tread. It appears to be completely fine, no missing paint, and no cut tread, and this is with a 0.75" drop. I also banged out the inner wheel wells just in case I could rub there, but no issues there either.

I would suggest using a wider offset, just because it's easier to roll the inner lip than try to troubleshoot rubbing on the inner wheel well, but it also matters whether you like the look or not. Mine barely peek out past the fender, but I've seen other cars (not performance cars) with the tires way out wide, and I personally don't like the look. It's up to you whether you can handle that.

BTW, does anybody make thicker sway bars for the xFire? I know they have them available for the MBs, but I'm not sure if we have the same suspension geometry (I don't think we do). That could help you out if you do end up rubbing, and I think that may be why I didn't have some of the problems other people did when going wide. More aggressive shocks would help as well.