Only mono's allowed in the Super Stock (stock) class as far as I know. Most run well with a stock Zenoah 260 so pick one. Yes, I know I'm not much help there. Some handle rough water better than others. It really is tough figuring out which one to buy as I looked at a lot of them before scoring a deal on a new RC Boatworks F-41. Before that I had an AC Model Boats Blast Cat 40, a Cat that really woke up in the rough stuff. My first Cat was a Falcon 41, really light but unfortunately no longer made.