I have read lots of good things about the GT3B, there is some forum somewhere they have made new firmware for it and it is as good/better then a spektrum. I plan on getting one!
I also have a Genesis Cat from HK. Great hull (I think, it's my first cat) It fast and turns sharp. I have however upgraded nearly everything in it. Motor, ESC, and just about to put in a new flex cable. All in all though, I can not complain. I have spent less then I would for a Spartan and I can drive 40 MPH all day without a problem. A simple motor and prop upgrade and it will push it into the 60's (I think. It's still only running a 36 can)
As far as HK producs, you can't beat the turnigy Lipo's and marine speed controllers (120A 180A and 80A-hv) for the price.