I'm not sure about all the processing/memory features of Live, but I can speak to the efficiency of FL studio, especially 10 and above. I run FL on both my monster machine (32 gigs of ddr3, 8cores (at) 4.8ghz), as well as a little 8-gig ddr3, intel i5 lappy. FL studio has a lot of "smart" processing such as "Auto Disable", the ability to ignore inactive i/o's, forced buffer sizes and offsets, the list goes on. All of these features make for a very efficient studio that can squeeze every last drop of juice out of any machine.
Another great feature of FL studio is it's method of core/thread use. If you had a 4-core machine, the main mixer tracks are tasked out to all 4 cores evenly (or 2, 6, 8...etc), thus always ensuring an even load. This means you can have a lot of tracks without
necessarily blowing up your system resources.
As a tip, an easy way to avoid the quick Ram and CPU death that a load of VSTs can cause, is to simply render a VST track to audio as soon as you're done composing with it. It's far lighter on the system to play an audio file than live processing a fully-effected VST synth/sampler.
Hope some of this helped.