well hydros are generally faster than cats (yes before you shoot me down, I know that this is a super huge generalisation - but let's say that all other things are equal, and the water is flat), but they don't work very well unless they're on a plane. Now i'm guessing that with a gas boat in tow it's gonna be hard to get a hydro on a plane, more like a chug chug chug and the nose is under the water half the time. With a cat I'm thinking you could have it double as a rescue boat, as it'll let you abuse it more at lower speeds. Also, using nimh cells you're gonna have plenty of room in the sponsons of the cat, whilst with a hydro, getting the setup right might be tricky, particularly with a gas boat in tow....good luck, and let us know what you decide....

Andrew