Dell UK Options (XPS 720) - ideas needed

I have been asked to purchase, from the Dell site, the best non H2C configuration on offer.

That makes the choice quite simple - the XPS 720 (dell.co.uk)

It would be used for gaming and for video editing.

To that end, I have a few questions:

• Does 4096MB of 800MHz RAM perform much better than the same amount of 667MHz RAM?

• Would it be better to have the standard 500GB HDD setup (16MB Databurst Cache) or the 250GB HDD, with SecureData Backup (2 x 250GB)? I am inclined towards the larger, single drive - for the editing - but is the security of another HDD necessary (as I almost never use that amount, for non video material)?

• Dual 512 MB Nvidia GeForce 8800 GT or Single 768 MB Nvidia GeForce 8800 GTX? Why? I looked at cards, rated on this site, and (based on overall fps on a number of games), the 8800 GT is not far behind the GTX. Surely two GTs must be better, yet the more expensive setups have the single GTX. What am I missing?

• Blu-Ray drives (considering it is now the dominant HD format)?

One key reason that I am being asked to purchase from Dell is because of the customer service. Take this out of the equation and is there another major manufacturer, that can offer the same or a better specced (versus Dell XPS 720) pc, for the same or a cheaper price.

If you have the time, I'd appreciate a reason for each response. Thanks a lot

I suppose the dual versus single was the most important question, but I did want to read answers to the others. Thanks for being thorough.