I've wondered if Athlon XP notebooks perform well. They sometimes use VIA chipsets and undoubtedly have many power management features implemented.
I have an Athlon XP based notebook: a Packard Bell PB07 (which I believe is a rebranded NEC Versa C200) and it's a real piece of shit. My family nicknamed it "the dragon" because of how hot it gets, with the loud fan coming on as its 'breaths of fire'.
It's very heavy but not very sturdy, the case is cracked around the hinges, it runs very slow even with lots of RAM, it literally kills batteries, as in the lithium cells go completely shorted (I guess it's a combination of heat and high power draw), runs off a humongous brick that doubles as a foot warmer, no built-in WiFi (and the mini-PCI slot is not populated nor operational), I used it with a PCMCIA WiFi card and I had to resolder the PCMCIA slot every couple of months because it'd get so damn hot the slot would desolder itself. The horrible Insyde H2O BIOS is hardcoded to downlock the CPU to ~600MHz when on battery and it can't be overridden through any means (I guess that's their 'fix' for the 5 minute battery life at full speed), did I mention it gets really really hot? One time it decided to randomly turn itself on in the middle of the night and since I put the lid down when not using it the LCD is noticeably darkened on the area that sits on top of the CPU when closed. It gets that hot.
My mom got it as part of a debt payment back in 2007 or so, XP runs dog slow on it and it won't do Vista/7 (corrupted graphics and no updated driver). I feel bad for whoever bought this at retail, it's a horrible machine. I feel like I should review/benchmark it or something just to show the world how awful it is.