jay2tall :
I run (2) GTX970's in SLI and it runs around 60FPS and dips often to as low as 40FPS. I play the Breaking Point mod exclusively. I was astonished by the FPS dipping on Ultra so I disabled a card and ran a single card to test. I get around 30FPS on Ultra with one card. My system is in the sign. So you are right on target, try running VERY HIGH or HIGH settings. You can also try setting the HIGH template and change a few detail to higher settings until you get to a good balance. I notice a lot of frame dropping when areas are more populated with players. It's very CPU intensive, but in general I think it's just poorly optimized.
It's not really poorly optimized, though. if you play in single player, this is noticeable. The multiplayer aspect is just highly limited due to the insane amount of calculations the server has to do, plus with 30-100 players, sending out the information, receiving it back, etc.
If you think DDOS's are bad, these servers are pretty much the definition of abused. Hell, i played on an island life server, which didn't offer AI, and I still managed to use about 1GB in data in about 30 minutes of playing.
There's just a lot happening that the ARMA 3 server synchronizes to the players. Optimization is also partly the server administrators fault, as ARMA 3 is built with the ability to configure the software to adapt to ever changing technology. A prime example of this is the use of a Headless client, which wasn't even officially supported but was infact created by players of ARMA 2 to allow the offloading of AI calculations to a secondary server, allowing the AI to react faster and increase the FPS of the server.
In all honesty, the fact that ARMA even runs in multiplayer is a miracle to me, when you have games like BF4 that can't even get basic things like invisible walls to not show up in their games....