I'm not going to bother reading the whole thread, but I'll say this. Earlier this summer there was a city singles tournament and the guy who won it almost exclusively uses a slice forehand. This is a kid who plays second singles at a DI school (U. Toledo) so he's no slouch. If I were to give him an NTRP I would estimate 5.0? So yeah, I think you could say that the slice forehand works at high levels if you know how to use it.
All aboard the Gulbis bandwagon!