It's not worth going crossfire for cards like HD 7750/7770. Go for single card like HD 7870.
Furthermore, if you'd like to repair this card from overheating, it wouldn't be hard at all. You'd need to buy some hermal paste (costs $5-10), remove the cards heatsink, clean old thermal paste with rubbing/isopropyl alcohol, apply new thermal paste and put the old heatsink back. That's it!