Hi Aaron,
Never heard of GT casting SMP however the GT max power plus is arguably the best solid core braid on the market. I'm not too sure that Varivas have a hollow core braid?
As for the casting SMP, it's the same as the casting MP but has a higher breaking strain rating so it can be used for IGFA records.
In my opinion, the wax on SMP creates more wind knots than any other line I have used/seen. That's if your casting with leader through the guides. The wax is simply too slippery and it catches up to the leader before it's left the guides and creates some truly terrible wind knots.
Cheers
Rich