Our kids are in a GT Magnet, where the GT kids are (mostly) in separate classes all of the time. This is socially wonderful, because I'd say there are at least 5-6 truly HG kids in each grade level, so socially my kids have lots of options.
I looked into a very small private school nearby, which has 1 class per grade level and a very open attitude toward acceleration, but when I asked the principal about peer groups, she was very honest and told me that, based solely on test scores, there wouldn't be any true intellectual peers for my kids. However, the environment was very warm and nurturing...I'm still tempted to switch at some point.
We're in the public for 2 reasons...1 it's less expensive, which gives us a larger budget for enrichment activities, and 2 there is a larger peer group for both kids. That said, I'm really frustrated with the attitude that because it's a GT program that must be acceleration enough, so forget about a grade skip, even though your kid is bored stiff... and don't worry, it will get more rigorous next year. I'm still waiting for that to happen.
There are pros and cons to both. In public school that only has a gifted pullout once a week, I'd have some reservations. I'd want to know how large the "gifted" population is at that school.