SLI (or CF) scaling in new card releases can change dramatically with driver updates. As someone who always reads the driver release notes, this is the area I notice most of the improvements which build up over time. I believe Nvidias top priority for their driver teams is single card performance for the reviews and SLI after that. But anway the numbers of 3+ GPU SLI owners is probably less than 1% so I doubt it matters in the overall scheme of thingshttp://uk.hardware.info/reviews/5623/nvidia-geforce-gtx-980-sli--3-way-sli--4-way-sli-review
SLI still has major issues with 3 and 4 card scaling.
1 = 27.6 (FPS) = 100%
2 = 52 = 88% scaling of the first card
3rd = 62 = 20% more total, = 36% scaling of the first card
4th = 71 = 14% more total, = 32% scaling of the first card
Basically cards 3 and 4 are throwing money down the drain. I'd like to see the comparable 290x tri and quad fire since I believe they usually scale a lot better.