You want to trade a 5870 for a 5850? Why?
Seems to be better off for the configuration I'm running. I like my above average results with 5850 that I had. I bought two 5870s while looking for 5850s. However I get at best the average medium on the results regardless of my best ability at tinkering. It seems like the 5870s have more value than the 5850s, so I'd like to work something out to my advantage or a deal of some kind for someone else who wants to trade up. I don't literally want to do a straight trade for a 5850 for one of my 5870s, but if I were to sell on eBay the fees after PayPal rip me up. Half my use of bitcoin is to get around this whole world.
Further I want to make a second machine for my girlfriend to run at her place and use when she needs it for school. 5850s are a little cheaper and run lower on power, so ideally I'd like to own four of them (I have one currently). I'd, for example, love to trade the two 5870s for three 5850s. I think that's close to market accuracy, no?