I have 285/30R19 at the rear, circumference is 1.70 % difference against stock. With 275/30R19 difference would be 0.76 % difference so even better.
Swedish laws allow up to 5 % difference in circumference, so both alternatives are well within legal range (for Sweden anyway).
The dimension I use is quite hard to come by at a reasonable price, the alternative suggested by Neil offers more options though. My choice was made with traction in mind, as I find tires of OEM dimensions sadly lacking in traction to say the least. These are better, but just barely and I would prefer having even wider tires.