Really?
Well maybe they should update their UK website so you can select a Quad Core Opteron as an option
Dell's Opteron experience hasn't been all that fantastic. After resisting the Opteron push for so long, Dell embraced AMD's flashy chip just as Intel started to catch up on performance and performance per watt metrics with Xeon. Then, Dell watched as AMD shot itself in the chest with the four-core Barcelona roll out. Dell was …
*** networking ***
in network performance tests, opterons have been shown to outperform core and xeon systems by a large margin.
http://article.gmane.org/gmane.comp.security.firewalls.pfsense.user/2738/match=opteron+xeon
*** power ***
although at peak, opterons use more power than intel's, at idle they are more efficient, and a single-core opteron *might* be better for your application.
** performance ***
it's also been found that a core2quad can sometimes be slower than a core2duo because of the contention on the front-side bus, so again, if your application is CPU bound with a single thread, you need to consider that an intel might not be ideal!