tbred a core had difficulty going past 2ghzish....more like 1.9ghzish..
thats why amd redid the core (well kinda, jst added a few more layers, etc) and introduced tbred b which is going way past 2ghz
in short, tbred a would hit a wall around 1.8-1.9ghz...maybe 2ghz
tbred b will go past....around2.2-2.3is somehwat normal with 2100+