52 FPS is very good if you consider the high demands ArmA2 has.
Depending on how much AI a mission has, or how many scripts are running at the same time a huge performance drop is not uncommon. If a mission has 200 AI units fighting each other and all kind of scripts checking things every 0.1 seconds also a NASA computer has a noticeable FPS drop.
3D Resolution is good enough if set to 100%, higher settings you wouldn't notice anyway. You need to play with your settings a bit as everyone has to until you found the perfect balance between good graphics and good performance.