Both sweet chips to have laying around. Tough choice lose the threading for newer architecture. I would go with the 3570 but i would be gaming.
i get better benchmarks and performance from the 2700 but it runs more hot when overclocked.. prob because its the non k.
Might keep the I5 and build new computer and use 2700 and sell it online.
Thats probably what i would do if i had them both. I have been holding for haswell myself.Nice rig those 660s probly outrun my 680
ive have the 660s for ever they do the job really well... they do run pretty hot without aftermarket cooling.... waiting for the 700 series to come out... should be really soon i hear