I got my X5650 for £60 and sold my i7-920 for £30. It sold immediately though, probably could've got £40 for it.True, I would assume an i7-920 would fetch maybe $10 to $15. It's honestly more valuable to you as a backup. I considered trying to sell my i7-930, but there's no market for it.
Never mind, apparently i7-920s are going for $40+ on eBay. It might be worth posting it on there if you can get that much.
Probably the best bang-for-buck upgrade I've ever done.