In general, a boat without a jib can point higher than a boat with a jib. It has always been my understanding -- from others and from just plain common sense -- that the jib bends the wind so that the mainsail sees the wind coming from a lower angle. And that is even with a well-sailed and tuned sloop rig. The worst, and most common, problem with sloop rigs is the jib backwinding the main, causing you to sail low and slow. With the fully-battened mains we have on cats, it is much more difficult to notice a backwinding situation than with the soft sails that most monohulls have.