If you don't want to mess around with overclocking just get the preclocked ones. the 7970 overclocks well. 2 7970's most likely wont need a overclock to perform well though
I would not normally mess around with OCing, but if it would save me almost $80-$100 (x2) I would OC. My questions would be, would OCing Card 1 to the specs of Card 2 be worth the savings of buying Card 1 over Card 2?