It's new tire time. I have the OEM 19's (front are 8" and rear is 8.5"). As you know, the OEM tires are 225/40/19 and the rears are 245/40/19. If I go onto the TireRack.com website, it says I can put 245/35/19 on the front and 275/35/19 on the rear. However, I called them and the guy on the phone said the max I can do on the rear is 255.

I've done a little research and there is conflicting information. Does anybody have a similar setup? Is it possible to put 275's on the rear?

Its possible, but not advised. The tire physically fits, but bulges and is a possible safety concern because its outside of the safe operating range recommended by the manufacturer.

its really not safe at all just go with 255

this topic has been discussed and debated extensively:
https://g35driver.com/forums/wheels-tires/73638-275-s-oem-19-s.html

bottom line is, they will fit but they look meaty and probably less safe than smaller sizes

Just got them done on my G35. There's less noise now and it feel more smoother riding. Sure they budge like you say, but not that much. Also the tire installer that was putting on this tire's, Didn't have any problem putting on this tire's. Did them fast.