i have these wheels and run the stock sizes. r888 do run wide, probably could get away with 205/45 and 235/40. Although, if I was buying new tires it would be r888r, not r888. Depending on how much power you have, more than stock sizing might be unnecessary - wider heavier tires translates into less top end down any given straight, unless you have the hp to minimize the trade off.
"Give a man a match, and he'll be warm for a minute, but set him on fire, and he'll be warm for the rest of his life."