I would imagine that Tri SLI would be absolutely brutally fast on the gtx 280! I wonder if a 1000W PSU could do it, or if you'd need more than that.
I guess also we will find out aproximate HD4870x2 performance levels from the reviews when they come out. Im sure they will be able to do Xfire and Sli to check out the scaling as well.
Tease.