Hello ! I'd like a little help in diagnosing a performance issue during battles :
The specs :
e8400 cpu
gigabyte ep43 ds3l mobo
3 gigs ddr2 6400 ram
512 mb 9800gtx graphic card
sata 7200rpm hd
-native : runs perfectly fine and fluid with no issue whatsoever on a battlesizer of 400
-floris expanded (i use to play basic before and loved it, just got that e8400 system so trying the expanded... OH WOW IT'S EVEN BETTER

) i ran different test to corner the problem:
Open battle (quick setup with custom battle):
200vs200 : the frame rate is ok, perfectly fluid while it moves BUT there's a micro stutter: every 1,5 sec it freezes for a couple millisecs or something.
160vs160: same but the freeze last noticeably less, it's almost not perceptible
Once again note the framerate is fluid, it's not that I have low fps, it's that every 1,5 sec or so there is no movement at all!
It seems to have nothing to do with graphics :
-I've tried various combination of texture and character details, from 30% to a 100%, and everything else rather low, but that does not changes anything
-I've changed the particle system back to native, but it dosnt change anything
- I've tried mixed and pure infantry battles, they do just the same
-I've put the textures minimods which remove normal maps (whatever they are :p) but it dosnt change anything performance-wise
-and the game is perfectly fluid on sieges ! even 200vs200 !
-the freeze subdue then completely dissapear as soldiers die
So that'd seem to point to a AI load problem on field battle, dosnt it? Are any new AI features from floris known to eat significantly more cpu than native ?
All tests are done in custom battle mod. I'd like to tweak the game to playable 400 battle sizer before I start

thanks !
edit: tried also with all AI fix option off, still the same thing.