That'll work just fine. A 275/50 is plenty of tire for you right now looking at your mods in your sig. Check out Centerline Telstars, too. They are good looking wheels and cheaper than Prostars by a little bit and not as common and available in 15x8 with 5.5" BS. I've had both in the past and liked my Telstars better.
Edit: Disregard that comment about the Telstars. Holy crap! Apparently prices have changed. I just checked some old notes and I bought 2 15x4s and 2 15x8s for $515 from Jegs in the summer of '04. I just priced the same thing at Jegs and it was $1023.96. They used to be cheaper. Pretty sure they used to be available in 5.5" BS too, but not anymore. They have them in 5" which should still work just fine. On my old '04 Cobra I had 15x8 Telstars with 4.5" backspacing with a 275/50-15 and the fit perfect, didn't rub, or stick out. I used them with the IRS and the solid axle I later put in. No probs. with either.