Sorry digging this thread, but I liked the game despite the suffering from low fps.
Read the guide below and could squeeze few more fps from my AMD rig.
http://wiki.day0.com.au/ArmA_3_Performance_Tweaks_and_Settings_Guide
My rig has some kind of issue for sure, since Firestrike score are way below the average.
Probably the MB.
http://www.overclock.net/t/1202751/amd-fx-cpu-throttling-fixes-please-sticky
Anyway, view distance had the major impact.