Getting bad fps drops in battles/randomly

[Pud]

AMD Phenom II X6 1055T 2.2
8GB corsair DDR3 RAM
and a gtx 560ti

My rig isn't THAT OLD and the fps drops sometimes to 15 completely random, i could be in the same huge team vs team and my fps is at 80 then other times low as hell, and sometimes it will drop for no reason.I've tried playing with the settings and the same thing will happen, is this an engine issue or ...?

Thanks.

Edit: Also when i use console to disconnect i get 'x memory leak in client'

[Space Wolf Hudson]

Things that increased my framerate (beside of set some of the settings to low):

change the process-priority of NS2 to high (task manager)
activate Vsync
activate texture streaming
activate multicore rendering

and last but not least: using organic alien overhaul texture mod (have a look at the link below)

http://steamcommunity.com/sharedfiles/filedetails/?id=118315718

The screenshots there are a bit outdated though, everything looks a bit different now and the textures got a higher resolution