Well first off what psu are you running this off, since your current card requires very little juice, And a newer one would need a lot more.
But if you have the right psu, a4850/70 would b a great upgrade.
And as far as overclocking goes. Im not familiar with that motherboard, but with a ''decent'' motherboard you could hit 3.2 rather easy. My old e6400 (2,13ghz) Did 3.4 so you could probably hit around that, if not higher
But first things first Check your psu