I experienced the same, the first few days after Altis was released the performance was good. Especially switching to units further away was almost instantaneous, now it freezes the game for a few seconds until the area has fully loaded (depending on the view distance). Using UAVs and UGVs is really frustrating now.

I have the same issue. it started to become unplayable the same update that brought heavy armour to the dev build and hasnt been sorted since. if I dare get into an aircraft over altis it becomes totaly unplayable and has ruined the game for me. Before this update i always had my view distance set to 5K and never had an issue. minimum fps was in the 40's now if im in the centre of the island i can get less than 0 if i just spin on the spot in an empty editor. i can see the hills in the distance appear white with a lack of textures and then they load correctly but if i move the mouse to look elsewhere the game freezes again to load more textures. the whole time my GPU isnt being used more than 40-50% and my CPU isnt breaking 60% total and no one core/thread is breaking 80%. some arent ever being used more than 10%. currently i have to keep my view distance to 1000-2000 metres to keep my fps playable but that means playing with the annoying fog of war constantly visible. if im airborne i need to play less than 1000 metres view which is pointless because it means i cant see anything until its too close to manurer. my FPS at 1-2K metres is way over 100 but drastically drops off at little over this distance making the game unplayable again but without actualy using much more of the system. totally ruining the game.

An Update: I've experienced much-improved performance with the "retail build" currently out, but that build is two weeks older than the dev build that, for me, brought all of the issues out in the first place. I fear that, when the backlog of dev "fixes" are brought back, it may go back to slideshow territory.

In the meantime, however, I found that I was able to cheat an extra 25 to 30fps out of the game doing three things One, open the task manager and set the Arma III process to highest, two, lower SSAO to "standard", and three, reduce my view distance from the auto-detect setting of 3800 to 3000. I went from 30-35 fps (on the retail build!) to 55-60fps! I saw drops into the 40s when entering towns and such, but it's a MASSIVE improvement over what I had last week!

Yeah, that 32bit memory improvement really lowered my fps and stability. Well atleast I think it was that memory fix, as that update made my performance worse. I'm on win 7 64 bit.
The irony is that all the way through alpha and beta I haven't had a single crash! Not One! But now, just before release and after, it's crashing every now and then.
nvm about the crashes, may be related to radeonpro.