I'm considering acquiring a 2nd gtx 670 and SLI it with the one I currently own. Few questions: 1- They can be from different manufacturers, as long as they have the same amount of VRAM, right? 2- Would you suggest any particular manufacturer/model? The one I own is this. 3- An i5 2500k @ 4.2Ghz won't bottleneck them, right? 4- Are there any issues I should be aware of?