best way to minimize risk in silicone lottery with GPU's is to look at the overclocks people are getting with 7850's. Whichever brand seems to be getting the better overclocks, is generally the brand that's using the best PCB's and will give you the highest win % on the lottery. I guess japanese capacitors would be something to look for too, but some manufacturers will give an unwarrented price gouge just for those, so be watchful on that.
Saphire gave me a good little 6750 ~3 years ago, that things still doing real well, brother is using it as an interim card since he sold his 6870 and saving up for a 7000 series.