c5er

I am down to two tire choices; Nitto Ridge Grapplers and Cooper S/T Maxx, but leaning towards the Coopers. I was set to go with a 34/35" tire (per spec) and a 17" wheel, however my only real choice in the cooper for a 17 is a 285/75R17 which us 34 tall x 11.1 wide. However they do have a 295/70r18 which is at 34.25x12, or a 305/70r18 35x12.5 which I think is a good size. The main reason for going with a 17 over an 18 has been more tires choices available. Now that it looks like the tire choice is dictating the 18" wheel is there any other downsides to an 18 vs 17. Should I move on to different tire to stay in the 17" wheel?