Fps too low or normal?

[unpurspy]

Well ,i've a 7800gtx 2gb of ram and amd athlon 4000+ and when i run the game with environmental effects on my fps seems really low(between 21 and 30 on external view depending on the weather).Below each time i set up an attack it'll drop way lower at times during the battle when ships are close to me(drop of 5 and not long but in each battles sometimes 10-15 fps)=(this last drop may be due to the "monolith" bug).When i leave pearl harbor i've got about 23 fps(external)
I could play without this effect and everithing would be smooth an all all times but i really like the pictures much better with it so i'll just avoid it if no other way
I've read all threads about settings but i d't know much about more recent graphic cards and processors so i've got a hard time to compare.
also i play with v-synch(ini tweak) and 1280x1024 resolution.
Could someone who knows pc configs better or with equal config tells me if these are ok fps with my rigs and wht to try if not?
Thx all and forgive my english