No problem ....
With an 890FX and DDR3 1333 you can run 14x250MHz at 1.375v with the IMC/NB at 2500MHz and 1.2v or less . That should give you an easy 15-20% on your frame rates. Your biggest problem is your power supply (assuming you are going with the HD69
Use 150w for the remaining system load (OC'ed)
edit --- I'm now firmly on the fence
I think you can use your PSU and go with the HD69502GB but
Using PowerTune you will need to find a 'sweet spot' somewhere between 210-230w for your video card. You will most likely need a new PSU when you flash that second BIOS to a 6970 and boost the the volts a bit.
A new PSU would also give you some room for 14.5x250MHz at 1.4v.