I haven't ridden the new GTI Gen2 Polytech hull on the GTR, so can't offer advise on that.
I have ridden the RXT 300 with the ST3 and it "grips" much more than than my 2012 GTI. If you turn, you better hold on, because it's turning with or without you. The GTI will slide a bit before the sponsons grab hold.
Rxt hulls s3 and t3 are like glue in the water. They turn when and where ever you want. Like someone said here, it will turn with or without you! Super fun!