I sure hope this can be addressed with high priority. Shortcomings in functionality or behavior can often be fixed by modders and scripters, but this is a core engine issue and as such can only be fixed by BIS. An issue like this that affects so many people and causes such frustration can only spell bad news for the game and its popularity if it is not fixed.
I love Arma, and have successfully referred multiple friends to buy the Arma 3 alpha. However, knowing from experience that this was an issue in Arma 2 and now finding out that the BIS developers shrugged it off in the past makes me concerned that they will do so again, and thus makes me reticent to continue recommending it lest I be causing people to waste their money. It sure would be nice to have some kind of official acknowledgement that the issue is being looked into seriously at least.
My observations:
I get an average of 50-55 FPS in single-player mode, and a nice smooth frame rate, even with a bunch of AI. When I start a server ("dedicated" on another machine or via "New..." on the multiplayer screen) with a very simple mission and just a few AI, I see a decent and smooth 35-45 FPS for a few minutes, followed by frame rates of 25-30 FPS with a high level of choppiness - constant, repeated downward spikes to 12 and even 8 FPS. Every time the frame rate spikes downward, the GPU usage spikes downward as well. Recording GPU usage and FPS using Afterburner and then analyzing it in detail shows that the downward spikes in FPS exactly match up with downward spikes in GPU usage (to 30-40%). When I join multiplayer servers with say 10-15 other players and a good number of AI, I get a low but smooth 20-30 FPS for a few minutes followed by the same choppiness, but the FPS downward spikes occasionally reach as low as 3 FPS.
Changing graphics settings does not significantly affect the FPS average or the choppiness. I have tried messing with command line parameters and changing GPU_DetectedFramesAhead and related settings in the config, with no major difference. My CPU usage is not high and I don't seem to even max out a single core - I see one core with maybe 70% usage and one or two other cores with 30-40% usage.
Machine:
Alienware M17x R3
2nd gen i7 2760QM (quad core, 2.4GHZ / 3.5GHZ turbo)
GeForce GTX 560M w/1.5GB, driver v. 314.07 - mildly overclocked to 860 core + 1401 memory
8 GB DDR3 PC1333 RAM
Issues happen whether or not I overclock the GPU, and it's not heat issues because the clock speeds remain constant and the component temperatures are well within the normal range.