that came as a pleasant surprise is the SLI scaling with the newely announced Nvidia Geforce GTS 450 card. Despite the fact that Nvidia marketed the card as the "perfect LAN party GPU" for 1680x1050 resolution, two of these in SLI are doing quite well at higher resolutions. Scaling in Crossfire and SLI was always a problem and you could rarely justify the price of getting two cards compared to a single, more powerful card.
This time around, Nvidia Geforce GTS 450 does its job quite well and the guys at Techpowerup.com paired these two to see is there any value in SLI configurations with these cards. The SLI scaling gain goes from 60 percent at 1024x768 resolution to up to 84 percent at 1920x1200 and 2560x1600 resolutions. The GTS 450 SLI outperforms ATI Radeon HD 5850 and sells for almost the same price, as the lowest price for the HD 5850 stands at US $259.99, and two GTS 450 cards can be yours for around US $260.
To make things worse, the GTS 450 SLI comes close to the Geforce GTX 470 which sell for US $279.99. The obvious drawbacks are higher power consumption, noise and temperatures, which are usually higher in multi-GPU configurations rather than on single GPU card.
It might make sense to buy a single GTS 450 now and leave room for another once the price goes down. You can check out the full SLI scaling review here