Which would be better for my 28' Pantera? 540 @ 650hp.

A B1 should give you plenty of bow lift, w/a better cruise speed.
I think most 28s are running a 4 or 5 blade.

that's what I've learned

They're heavy boats. I don't think a 3 blade would have enough blade area.

I've never heard of anyone running a 3 blade on a 28. It would probably blow out too easy.

4 blade

Tried a 5 blade... didn't really get to push it but I really liked the results. My B1 is really slippy to the point where the boat really feels like it needs another prop in the water (if it didn't kill that amazing balance), but from the little I got to run the 5 blade, it felt like exactly what the doctor ordered.