[LAU] Resource gains - lightweight Desktop vs KDE, Gnome

Hi all, To refine the question a bit; Older laptops in this case... 1.6ghz - 2.2ghz dual core 64bit processors and their rough equivalents, running say, current KDE4 Ubuntu like environment, vs flux/blackbox <add ur choice here>, etc. anyone got any real results? Like, I want to record at 128/2 ... Can I run a softsynth or Jammin on top of a few live plugins running simultaneously kind of difference or ... The point I'm subtly pointing toward... Does the lightweight WM or DT really give me anymore power to do something useful?? The only user difference in experience, for the most part that I see, is losing the automated bells n kazoo's tht heavy desktops handle. Of course there's more but I'm just curious about case examples with something to back them up & not be centered wholly on opinion. ~ Russell