Hi Robert,
How's your German?
Looking for a RTR in the US could prove to be very costly...
And the fastest electrics are made in Europe!
Take a look at these links:
www.hopf-modelltechnik.de
www.hydromarine.de
www.kehrer-modellbau.de
www.mhz-engines.com
Also look for a club in your neighbourhood and get some advice there.
The "fastest" RTR boats you can get are much slower than the boats from the manufacturers I listed above and are much much more expensive.
All these manufacturers can get you all you need to put a fast boat together and you'll have to be all thumbs to get it wrong.
Mind you they don't provide kits, like robbe and Graupner do, they ship you what you need to assemble/build the boat yourself.
When you read German, ask around on these forums, you can write in English if you like, no problem.
www.rc-raceboats.de/forum
www.hydroworld.de
Mail me if you have more questions.
Regards, Jan.