I'd finely tuned OA/CO and had it working nicely at around 2000-3000 Visibile distance but I recently was playing a chopper mission so upped it to around 6000 for that.
Then I forgot to reduce it and started a Battlefield LAN game and it was unplayably jerky right at the start inside the compund. I'd recently installed GameBooster so Alt-tabbed out and put it into Boost mode and was delighted that it got rid of all the jerkiness, so now I can play ground missions with 6000 visible distance as well. I haven't got round to measuring the FPS yet, but it seems fine to me, so I just wanted to share this tip in case it helps others.
All Gamebooster does is stop some services and clean the RAM, so I'm not sure which services being stopped gives the boost but I don't really care. I like that it lets me restart all the services with one click as well, rather than having to mess around in Services turning them off/on manually.