I run 38 psi in both my 225/45R18 & 215/45R17 RE003s, lower profile and performance tyres are designed to be run at higher pressures and are certainly more fuel efficient when they are correctly inflated.
You obviously want to be careful how much pressure you run as you don't want to end up either, a) under inflating and wearing out the outside of the tread / side wall damage or, b) over inflating and wearing out the middle section of your tread.
38 psi is a personal preference, best you find the correct pressure and most economical for your tyre by doing the testing you proposed.