Having dual processors speeds OSX up tremendously as it divides applications and OS functions up between processors. You wont suffer lags or slowdowns as you do when running a single proc. Both computers are very fast, and depending on what you are doing, they should both suit your needs more than adequately, with that in mind, the dual 867 is likely cheeper, and deffinetly a better buy than the single gig.
EDIT: Once I looked at the systems you linked to I noticed that the gig was labled as having an OSX boot up, if this is the case, that means that this is one of the new Macs that CANT boot classic. Fuck that! Stick with the 867.
Classic is still a usefull OS nomatter what crapple says.
[ March 02, 2003: Message edited by: psyjax: plain 'ol psyjax ]