Ann and I are around 350lbs (probably a bit more after Christmas!), and I like to think we're competitive.
We do definitely struggle in the lighter stuff, but if it's enough to get one of us on the trapeze we're fine and by the time we're twin-wiring we're laughing.
As Tim says, poor boat handling is far more likely to lose you time than a few extra pies. That's certainly what I keep telling myself, not least because practising sailing is much more fun than dieting

Paul