An update: I've run into trouble running the E1705 w/ 7900gs at 600/800.
The laptop itself runs at this speed perfectly stable and with acceptable (although sometimes rather hot) temperatures, but it's the power supply (power brick, AC adapter, whatever) that can't keep up.
In some conditions, the AC adapter simply switches off, cutting power to the notebook. It only turns on again if it is unplugged and plugged in again.
In other words, if you want to overclock your E1705 up to 600/800 and remain stable, it looks like you're going to need an XPS power supply.
*NOTE*: This only happens when BOTH CPU cores are being maxed out. So some games won't have this problem unless you're running something in the background. It happens to me while playing Rainbow Six: Vegas, which uses the Unreal 3 engine and supports dual-core processors. I was hosting a LAN game at the time, further increasing CPU usage.
Luckily, XPS power supplies are pretty cheap :P