Nemesis, you can see my system in my signature.
Last night Aerobatics Online Server was too crowd for me actually. You can guess. I played nice. More than a couple times I experienced server-quake, long freezes.
Later, I went another server with Syria map, with no much pilots - and I did fly for hours, between 20~30~40ish FPS.
If you ask my opinion, and if we do compare, Apache has no FPS impact on my system. Very similar with other modules (A-10C II, Ka-50, F-16, F-18...)