I just built a new PC with windows 8 and I can say it is significantly LESS demanding on resources.

with 8gb of RAM windows 7 bare install occupied 17-19% of ram, while windows 8 occupies 14% ram and consumes less cpu cycles.

I was hesitant about upgrading to 8, but it was well worth it. It is also extremely stable. No crashes in the 4 months the PC has been assembled.