Moptop,
I size my cast bullets .358", and even use some at .359" in my 9mm pistols. My Beretta has a groove diameter of .3572", so for me the defacto .356" diameter std for cast/plated is not what works for me, results in leading and not so good accuracy. For cast bullets, if the round will chamber OK and not hang up because of being too "fat", the bullet diameter is OK. In the jacketed arena, I'd give the .356" bullets a try and even .357" "38 bullets" depending out what you find out after barrel slugging.
Although the typical 9mm's twist rate is too fast (1:9/1:10) IMO, it sure does not help the situation that most ammo is made with bullets that are not the proper size for a lot of the barrels used.