The AMD 64 has better potential for 64 bit (Pentium M Centrion like the Dell 8600 is only 32 bit) but it is heavier and a bit hotter as well.

The new AMD Turion 64 models (HPshopping.com has both AMD 64 models and Turion models) has somewhat better efficiency and less heat (low voltage cpu) but still not to the performance of the Pentium M Centrino (but that is 32 bit).

Note that the HPDV4000 series also at hpshopping.com is the new model equivalent of the Dell 6000 (replacement for the Dell 8600) with the Pentium M Sonoma chips. However, it does not have a dedicated video card option yet as the Dell 6000 series has. But the HP does have the remote control PC card and the instant on functions for the DVD and CD player.
Again, these will run 3.5 to 5 hours on battery on the 6 cell battery or up to double that on the 12 cell battery option but they are 32 bit.

If you are willing to spend a bit more money and want a dedicated video card and definitely don't want to consider the Dell 6000 in a Pentium M look at the AMD based Acer Ferrari model .........