Anyway, eventually dragged my ass and loads of PC kit and games down to Horsham and then proceeded to spend the weekend indulging in lots on LAN and online gaming - much Call of Duty, Doom 3, Halo and, most enjoyably, for me anyway, cooperative Vietcong (Sat Cong! Sat Cong!).
We also did a fair bit of comparing Doom 3 performance on our systems. Conclusion: not a huge amount of visible difference between Low, Medium and High quality modes (didn't feel brave enough to try Very High): in each case, it dark, real dark, damn dark and when it's not, it still looks gorgeous! Concluded that Far Cry's tropical island locations were more attractive though ;-)
Anyway, now back home and waiting for me: Post Office missed delivery card which should be my Babylon 5 movie boxed set (Hooyah!) and terms and conditions forms for taking part in a 3G trial (double Hooyah!).