The
BEST video card as of the moment, no matter what the price is, IMO, the RX800XT-PE. It has lower power requirements (93 WATTS compared to the 6800's @ 105-110 WATTS), has faster outright performance, better driver support, and better cooling. Unless you really have an
excellent Power Supply Unit (PSU) such as an Enermax 475W, you might wanna consider the RX800XT.
SLI or Scalable Link Interface is a
technology created by nVidia to satisfy the needs of hardcore gamers and game developers alike. In simple terms, SLI uses special motherboards (SLI compatible) that have 2 PCI Express slots for the video cards.
Similar and high-end video cards should be used to obtain the best performance. These cards are then linked together by a "linker." It's having two 6800 GT/Ultra's or 6600's or X800XT's or 9800XT's in a single system.
The last time I heard about this promising SLI technology is that Gigabyte has just released a
dual-GPU 6600 that is compatible with SLI mobos. It's now having
4 video cards in a single system.