Arma runs more on the CPU side of things rather than GPU. A good CPU is the best cure for FPS issues. I was running probably average 25FPS throughout the OP tonight. What CPU do you have?
The CPU isn't the issue. I could run 20-25 fps during ops with my old video card. After replacing the old one with a 970ftw my fps dropped to around 2. This only happened on the official server and only during the op. After the op on the same server with the same template I got 60 fps. On all the other servers we have that I tried I gained FPS after putting the new card in. The issue is/was only on the official server while the op was running. The only way I can test to see if it somehow fixed itself is to try it during the op next weekend.
This has been happening occasionally with 1.62, I don't have an exact cause yet, but for me it will occur when there's several scripts running and AI being processed on both serverside and through Zeus. FPS will drop to an extreme low and the game will basically lock up and need to be killed through task manager. Again, no exact cause, but chalk it up to Arma being goddamn Arma.
Yeah, I've read on the BIS forums of people having similar issues, but not quite the same as mine. Theirs was fixed by simply restarting the game.
I'm starting to think it was some network issue because my ping to the official server was around 150 while the problem was happening. Though not an absurdly high ping, it was higher than normal. But I picked a random public server running invade and annex with no mods and 50+ players + AI and was getting fps in the 30's, then loaded up our mods and tried the official server again and still got around 2 fps. After that I tried the unofficial havoc 1-3 server and was getting 40-50 fps depending on what direction I looked.
I think the only way I can be sure is to reinstall the game and mods all over again.