I just recently bought Arma 3 and have been playing on an Altis Life server. I'm assuming the server has mods in it. I put everything on the lowest settings even though my rig is decent. I get anywhere from 15-50 FPS on the servers I play on. My rig includes a Intel 4670K, GTX 780, 8GB Ram. I'm not sure if it's the server or my end. I've followed the Arma 3 tweak guide, but I don't notice any differences.