crossfire setup

[leaumat]

Hello,
i have a question about my crossfire.
everything looks fine in solo
with afr friendly on amd drivers
and maxed out on 1080p in game,
i went from 60 fps to 120 fps i didn't expect to double it so that's great !

But when i try to race against ai, it totally messes up...

with single card i could race with 40cars max on medium graphics setup,
(between 45 and 55 fps at start and gradually up to 60fps after the first/second lap depending on the track) without feeling lags.

With crossfire i can barely have 24 cars on medium graphics setup pp filter disabled, more car or higher graphics setup and it is totally laggy..

I tried many different setups but nothing enough stable..

my config: i7 2600k oc at 4,4ghz
crossfire r9 290x
16 gb ddr3

custom shader patch and sol 1.5 installed

Is someone had this problem and solved it ?
Any suggestion would be welcome !

thanks
leau