Finding a pond in north/central Berkshire County that combines decent average size with decent numbers is tough.
They're are a fair number of ponds that produce lots of perch, but they tend to be dinks, and there are some (e.g., Fish Pond) that produce a lot fewer but of larger average size.
If push came to shove, I'd probably say Burnett's Pond in Savoy is your best bet for a "blend" of decent size/numbers, but even that's marginal.