I've had several groups come and go, often with members of one group becoming core members of another.
1st - 3 core players, lasted 4 years
2nd - 3 core players, lasted 2 years
3rd - 7 core players, lasted 5 years
4th - 5 core players, lasted 2 years
(2 year gap of steady play)
5th - 3 core players, lasted 2 years
6th - 4 core players, lasted 1 year
7th (overlap during 6th group) - 2 core players, lasted 2 years
8th - 5 core players, lasted 3 years
9th (and current) - 5 core players, lasted 2 years so far
I've also been playing off an on with my kids & wife of late, and some short stints with my brother and some of his friends (usually about 3-4 players)