Just to summarize:

It seems that the 285/30R19 is a popular choice for the rear, even tho it is the absolute max you would want to mount on the OEM rim width. This tire is approximately 26" tall (same as OEM tire) and will look great staggered with the OEM 225/40R18 tire up front.

However, if you are also bumping the front tire up to 235/40R18 (which is taller than OEM), you should strongly consider also using a 35 aspect ratio tire in the rear, either 275mm or 285mm wide. I suggest this simply to maintain the original staggered Crossfire look, as a 30 aspect ratio tire in back (at least to me) will then appear too short.

Just my humble opinion.