I've run Hangouts on a 1st gen netbook (Asus EEE PC) without any performance issues.
The only times where performance could be an issue is when you are running a video conference call which technically Skype doesn't really supports (w/o a premium or business account).
It depends on allot of things if you are using some fancy super duper HD camera and hanging out with 10 other people all using the highest possible bit rate streaming also you'll need a good computer with graphics hardware that will support all the required features for hardware acceleration in Chrome.
Back then there was almost no video HW acceleration in hangouts anyhow (well in Chrome) not on the silly 1st gen Atom for sure and it still worked fairly well (at about 60% CPU usage IIRC) even with the 720p camera on the EEE PC.
And it's not that Skype would be any better in that regards Skype might have slightly bigger selection of video codecs (Google probably had too back when Google Talk had actually a thick client) but Hangouts is limited more or less to video streams that Chrome can handle which usually means current web video formats.
