Kind of solved the problem, atleast for me.
My cpu runs at 3.2 Ghz and 6 cores, but i don't know if the game uses all of them.
Anyway, i overclocked my CPU to 4.2 Ghz instead.
Game runs much better now, doesn't drop below 50 in imperial fleet.
But why do you have to OC the CPU to not get fps drops?