Price-performance in terms of value-for-money
I'll cover SLI as an upgrade path in the next article, which features 6600 GT as the showcase setup. However until then, now that we've got two SLI setups to compare with 6800 GT and 6800 Ultra, we can start to form a picture of value-for-money. Most consumers of SLI will want to be sure they're getting the best value from their investment, in terms of added performance. One way to measure that is by plotting the percentage increase in performance for both setups. I'll examine Half-Life 2 first.Half-Life 2 Performance Increases
Now when looking at the above graph, it's important to consider the processor used, since the results are dependant on CPU limitation. With FX-55, the fastest consumer x86 processor on the market today, especially for gamers, the Ultra starts hitting the CPU limitation early, even with a single card. Therefore adding a second board with that CPU is only buying you around ~45% in either mode.
Constrast that with the GTs who gain much more in their quest to make the CPU the limiting factor.
Therefore on all current CPUs with Half Life 2, since performance will only go down with slower CPUs and the performance with GTs in SLI (and indeed the performance of all the setups) will converge as a function of CPU power as it drops, GTs definitely have better value for your money than Ultras.
If you're using SLI as an upgrade path, you really need to consider the CPU you'll have when you do so. Anything slower than FX-55 and choosing 6800 GTs over Ultras is the sensible choice, at least taking Half-Life 2 as a benchmark. I'll cover all of that more detail in the next article with 6600 GTs, but start to bear it in mind as you think about SLI more closely.
Doom3 Performance Increases
For Doom3, the gains are massive for both Ultra and GT. Looking back at the frame rates, with GT shadowing Ultra closely, again we come to the conclusion that when considering 6800 Ultra vs 6800 GT, on a CPU up to and including the FX-55, the 6800 GT is the card to choose. Ultra in SLI offers more absolute framerate but the advantages over GT for the extra cost wind up making no case for itself as a sensible choice.
For the very deep of pockets only at this point in time, even with a monster CPU like FX-55 under the hood. The inherent CPU limitations in these next generation GPU architectures is highlighted acutely with SLI. There's performance to be had though, and it pays to be canny when you're choosing.
