I've done some testing of high quality, 5w-20 and 0w-20 synthetic oils in hot climates ....
Based on the results I've seen, I'd use a 0w-30 synthetic in Ford/Honda/Acura/Mazda engines and NOT a 5w-20 - even if it was a full synthetic. With the xw-20 oils, you are right on the ragged edge when it comes to maintaining full flow lubrication in the bearings. A 0w-30 synlube "brackets" the SAE 5w-20 recommendation and provides better cold weather protection AND better hot weather protection. The GC, 0w-30, the Mobil 1, 0w-30 and the Amsoil 0w-30 are all better ways to go, for a car you intend to keep for 10+ years. The Redline 5w-20 would also be fine, but it's as thick as a 10w-30 in terms of high temp, high shear viscosity @ 3.3 Cp.
It's a no-brainer as far as I'm concerned, and I was predisposed to thinking that xw-20 synthetics would be just fine to substitute for 5w-30 and 10w-30 conventional lubes.
Tooslick