Full SLI X16 and SLI is there a difference

The standard SLI is 8 pipelines per card and yours apparently is 16 pipelines per card.

you just beat me to the answer

A more complete answer:
the normal SLI motherboards split up the 16 lanes to 2 x 8 lanes when running in a SLI configuration. The "full x16 SLI" apparentely runs 2 x16 lanes in SLI (like this one). Now this sounds like a better solution but in reality for today gfx cards it does not make a difference (they cant even fill the 8 lanes). This might be interesting when not being able/ not wanting to run an SLI bridge.

Apart from that. you dont need SLI. The price increase (+ 100%) does not justify a small increase (max + 20%) to even decreases in avg. framerates. Stick to a NF4 (ultra) based mobo (like a DFI one). By the time you upgrade the next generation will be out and one new card will beat 2 SLIed cards (like 1 7900 GTX just outpaces 2 7800 GTX in SLI)

I would suggest you look at the interactive VGA charts right here on THG!

They are extreamly useful for situations like this, for example pick out SLI 7800gtx and a 7900 and compare the performance for games you like to play, this is very important as there is a large lack of consistancy between differrent games and how they handle SLI

for example the source engine is not very fond of SLI and will alot of time cause a decreae in performance over a single card where as other games such as battlefield 2 or quake 4 will yield as much as an 80 percent increase in performance, there are also alot of other factors to consider when getting SLI such as the resolution that you plan on playing games. Hihger resolutions generally gain more benifit from SLI then lower resolutions.