I currently have a MSI HD 6870. I would like to know from all you smart people on here if it would be better to crossfire another 6870 with my current one or buy a GTX 570? Would the Xfire be better then the single 570? The 580 and other similar cards are pretty much out of the question due to price at this time. And note that the 6870 is about $100 less then a 570. Thank you for any thoughts on this.