Is cgminer better than guiminer and barelyclocked?

Does it support voltage changes on a lot of cards? Do they have to be of the same model?
Im using guiminer + barelyclocked ATM, but with BC I cannot change voltage or memory clocks on my non-ref VTX3D HD 6850 (only trixx does that well but I can only increase it), on my Sapphire non-ref HD 5850s I can only OC GPU core to 900MHz (memory and voltage changing works fine).

How's with hashing speeds compared to guiminer?
Im getting 360 MHash/s per HD 5850 (@900/350)
and 225 Mhash/s for my HD 6850 (@850/750)
drivers are ati 11.5 as far as I remember