Update: Here is what our development team had to say. Based on Intels current design guidelines, the Intel Quad Core Extreme Processor should work on the XPS 700 motherboard. However, Intel revised the design guidelines for boards to be compatible with this quad core processor to decrease the signal impedance of the front side bus. This is different from the board specifications on the XPS 700. Also, Intel specifies that the Quad Core Extreme Processor needs 4 GTLREFs (GTLREF is reference voltage to the CPU front side bus to recognize signals as high or low for data coming to the bus) and the XPS 700 board has only two references. Intels revised design guidelines for the signal impedance change and the requirement for two additional GTLREFs to support its Quad Core processor caused Dell to make system-level board changes that have been implemented with the new XPS 710. With those changes, Intels new quad-core processors are fully supported on the XPS 710.

Here are the legal disclaimers:

Intel quad core processors may have stability/life expectancy issues when used on the XPS 700 because it lacks the required GTLREF support, or they may not work at all.
If you attempt to upgrade an XPS 700 with an Intel Quad Core Extreme Processor, we cannot guarantee that the Intel Quad Core Extreme Processor will work, nor will we provide support for quad core processor-related issues.

Readers have also asked about SLI memory support. No change at this point. We are investigating making changes to the BIOS to enable this support but currently, we only support memory up to 667MHz. It can be overclocked via nTune. I know we have only covered the Automatic overclocking portion of nTune up to this point. In the future, we will cover advanced overclocking on the blog.