I wanted to be able to rotate the tires since I'm running so much negative camber up front. -1 degree is around the level you start to see tire wear due to the camber on a street driven car, and since I'm at like -.9 now I'm pretty much right there. I'd say it was to keep from wearing out the rears, but with a plain jane 318, 904 auto, and 3.23's I don't spin those 275's much.
The tire selection in those sizes gets tricky too. 275/40/17 is a pretty common size, lots of options. From there it goes to a 285/40/17, a few options out there. Almost nothing in a 295/40, a few in 295/35 but that's only a 25" tall tire. Then it pretty much goes to 315/35/17, and not a ton of selection there either. Also keep in mind that if you want to go bigger than 295 you'll need a 10" rim or bigger, so the rallye's would be out because the biggest I've seen them in is 17x9.
With the B rear and 1" offset you could fit 295's without issue. Maybe even 315's if your backspacing was spot on, but again you'd need a 10 or 11" wide rim for that. I didn't see a point in going to 285/40/17 in the back vs the 275's, not enough of a difference to give up the ability to rotate the tires and a better selection at 275. They'd probably look better though, little more sidewall, little taller tire to have out back.