Hi ZoneIII, they still make Velvia 50, at least in the smaller formats. Unless of course you're referring to the original Velvia, which Velvia 50 replaced.

I too shoot Velvia 50 at EI 50 and Velvia 100 at EI 125.

Whether you want to call it ISO, ASA, or EI, it doesn't matter to me, but I agree that you shouldn't be afraid to experiment and expose your film the way that works best for your particular look.