Fair play and you kind of contradict yourself in the post after mine but let's not go there
YOUR BASKET
1 x
OcUK HD 7990 6144MB GDDR5 PCI-Express Graphics Card £719.99
Total : £731.39 (includes shipping : £9.50).
That is the price for a 7990 that OcUK have for sale (and a stonking card/good price). It is when you compare the 7990 (not a fair comparison but hey ho) to the Titan and you can see that Titan isn't so badly priced. A single card solution is always the better option for simple things like noise/power/support/heat, so for this, I can see why people would buy either a 690/7990/Titan. You can't dismiss those issues and I know my leg gets toasty warm after a few hours of gaming.
The 7990 has an average performance increase of 19% over a single Titan. The Titan has 6GB of VRAM (and I know you love a bit of VRAM

) and you can add a further 3 Titans, where you can only add 1 more 7990. You know as well as I do that 19% translates into very few frames per second.
Now after CF/SLI, it does get a little bit meh with scaling and you need some serious overclocks on a high end CPU to stop the bottleneck.
This is me looking outside the box from a complete neutral POV and money not being an object.