"Desktop Replacement" and 3 hour battery life are mutally exclusive. Ya want that much power, ya got 3 choices .... desktop replacement and short bettery life ...... decreased power and long battery life or desktop replacement and lugging around a car battery.
I'd either grab the best Asus I could afford, or find a Clevo distributor to build one for you:
Jack - thanks for the feedback. At this stage I'm willing to trade a bit of performance for some battery life. I was considering settling for a core i5. The better ones appear about 60% faster than my existing core 2 Duo T8300.