My pal Courtney and I have managed to hit Lake San Antonio a few times this year. It is wide open, as far as launching goes, as you can camp waterside pretty much anywhere along the north shore. This place is somthing to see (from a distance) on Labor day, sort of like Lake Havasu but condensed in size with a much higher PWC to human ratio! The last time I was there I think I was the only human there on Thursday night.
Sailing conditions tend to improve in the mid-late afternoon as far as I can tell. We have had several days of 3+mile double-trap screaming reaches there. It is fairly easy to get to also, being pretty centrally located. I give it a generally enthusiastic thumbs up.
Also look at Woodward Reservoir, and San Luis Reservoir.
We are planning a weekend soon, let me know if you are interested in joining us!