At my old job, I was initially running xp on a thinkpad with 2GB of ram and I never had any issues with performance. I was doing standard web development work and used a relatively lightweight editor.
I switched over to win7 on the same laptop and they gave me 4GB or ram. Using the same software, the system lagged so much I had to go back and upgrade to 6GB of ram just to get the PC running at the xp-level of performance.
Something was broken on your setup. I run Win7 on extremely resource-constrained computers (1GB RAM, Pentium III 1GHz) and it works considerably better than XP SP2. I've had the same experience on old-but-not-ancient (Pentium M 1.7GHz, 2GB RAM) machines as well as screamingly fast new boxes (3.4GHz quad-core i7 with 16GB RAM). Across the board, Windows 7 beats out XP SP2 in perceived performance, and I'd be willing to bet it does so in real performance too but I can't be bothered to benchmark.
That's entirely possible, I never bothered to look at the junk IT installed on it. I also used the base Aero interface, which I suspected was a resource hog. I never tried to optimize performance since memory was free.
I also haven't ran XP with less than 2gb of ram since 2005, so I don't know what kind of slowdown xp experiences under resource constraints.
But my perceived performance equilibrium was about 2gb with xp to 6gb with win7.
It sounds like your machine probably wasn't capable of running Aero on whatever IGP it had, more than anything. Aero Basic runs excellently on even really old stuff (and handles screen drawing much more intelligently than XP did, so it feels considerably snappier).
6GB sounds excessive for that situation, but if your IGP is getting testy about system memory, it seems likely that it'd require a hell of a lot to simulate decent behavior.
(Typed on my Toshiba Win7 netbook, with a 1.6GHz Atom, 1GB of RAM, and Aero running without a hitch.)
I switched over to win7 on the same laptop and they gave me 4GB or ram. Using the same software, the system lagged so much I had to go back and upgrade to 6GB of ram just to get the PC running at the xp-level of performance.