We go to Sunapee for a couple of weeks each summer. We've been there over the 4th, late July, mid-August, and over Labor Day. For the most part it is not ski-able after 9:00 in the morning on weekends. Sometimes during the week it can be OK later, especially around Labor Day when the crowds are mostly gone. And as with anywhere, the best water is just after it rains. The best area is in Georges Mills, especially if there is a north wind. There's a submerged course there, but I think it's a members only thing. The lake gets very rough on weekends especially, with a lot of Boston money riding around in big boats in circles really slowly. There is a fair number of die hard skiers out every morning from around 6:00 - 9:00. Some days you can run almost the length of the lake if you are early enough.
Sunapee is a very beautiful lake with the cleanest water you've ever seen. A chart of the lake is a necessity because there are rock formations all over the place, many just under the surface depending on the lake level. But everything is well marked. There are only a couple of places to launch, so we always rent a place with a dock or boathouse to avoid the hassle. We learned the hard way to confirm with the agent that whatever is there for securing your boat is up to the task. I was assured that the cleats were adequate at one place and the cleats and posts pulled out twice. I finally had to show them what to use and how to install them. Depending on where you stay there can be a lot of rollers. The inlets are pretty quiet and are no wake zones.
The area around there is really nice, lots of hiking, etc on Mt Sunapee. Decent restaurants, only one that is accessible by boat.
What lakes do you usually go to? We grew up on Lake Champlain, so Sunapee seemed small at first, but we like it there.