I honestly havent tried any of the clay smoothing techniques yet, but I will take into consideration your method!
Good luck using the FX helmet. After making the pep helmet, and comparing it to the FX, you could see alot of differences in appearence. You'd have to completly cut up and re-do the face if you want to make it somewhat accurate.
Im currently at the moment learning how to convert the shoulder bells, chest and shin/calf armor into pep so I can use as either a guide or use to make molds!
-TC