Andy, The P4 seems to have the extra processing power for things like video editing and multi-tasking ,with many windows open at once.... While having lots of power consumption causing plenty of heat (which is a little harder on the electronic components) It is always at the ready, and doesn't reduce its own power consumption as is one of the features of the M and it will still do everything thing the other will do just micro seconds slower .It seems it is designed to run longer ,cooler with what appears to be more of a self monitoring chipset for the "enhanced useage experience"
One of the things that can slow down any computer is when loading software ,you are asked if you want your programs to load faster, If you select yes it will load an icon in the system tray which actually will let that program use processing power to "run in the background" so if you have a full systray it will help to slow down your system.... I always keep mine to a minimum.
For most users anything much over a GHZ will not be totally utilized....unless your a GAMER or other high consumption processing programs where the extra horsepower will definately be used...
Now I'm not trying to talk anybody in or out of what they may want ,This is just what I understand the new M vs. P4 features to be.... Good Luck in your decesion!! /forums/images/graemlins/cool.gif
So depending on your use ,The extra speed of the hotter processor may not even be noticed..