My three favorite PvP activities are:
a) Hold something in their city;
b) Rath Strat, AV (resource win, via choke points and/or farming their graveyard); and
c) Turtle Domination, IoC (farming them at our General).

Ten is definitely more power than five.
And in venues of 40's or unlimited numbers, it's not going to hurt my side having that.
Plus having ten, does not preclude me from using half the team.

I personally was purely into PvE for Classic+Burning Crusade.
And very early WotLK switched entirely to PvP as my focus.
Nothing says I won't switch to PvE for the challenge, at some point.

I plan on setting up IS Boxer with three profiles per team.
Or characters sets, is a better word.
First five, second five, and all ten.
Then can run any team, either way with the same hotkeys.