Mobo Upgrade for X2 555 BE

Hello!

Im shopping around for an upgrade or 2 and would like some advice. My current setup is:

Biostar AM2+ TA790GX mobo
Phenom II x2 555BE unlocked to 4 cores
OCZ Gold 4GB DDR2 800mhz
Powercolor 6870 1GB
Be Quiet 530w PSU
Antec 300

Im slowly upgrading it, the RAM needs upping for which i need a new mobo but i dont want to lose the ACC on my Biostar as then ill have nice RAM but only 2 cores. Going for DDR3 CL7 1600Mhz, probably Corsair.
I understand that theres no garuntee a different mobo will succesfully unlock the extra 2 cores, but im looking to find out which ones give me a good chance.

Mobo needs AM3, DDR3 1600, ATX standard, SATA and USB 3 would be nice but not essential as i can always get a PCI upgrade. Onboard GPU doesnt matter. Crossfire...probably will stick with single cards for the future as i see so many problems relating to it so board doesnt need this.
I would prefer ACC, but i know Asus have their own feature too, and i think AsRock too?
Would like to have a few OC features on the board to for a cheeky boost to around 3.5Ghz maybe.

Budget....around £70 but can stretch it for something special.

Cheers in advance!