Which is better 2600 XP-M or 3000 XP?

Assuming I want to overclock which one should I get? They're both in the same price range and I know that the mobiles run cooler but the 3000 starts out a bit higher. Not going to upgrade for a couple of months as I first need to get the mobo working right, but when I do decide to upgrade, which one?

Yea, don't say move up to an A64 either, won't have the cash for that.

mobile all the way

Definately the mobile.
It may start at a slightly slower clock speed, but since your OCing it, it doesn't matter at all. The mobile is completely unlocked and runs at a lower voltage, both VERY important things to have for overclocking. The 3000 you are talking about I'm assuming is a desktop chip so it probably won't be unlocked and probably will not OC as high.

The mobiles "start" at 600 MHz, that's not the point, in the end they clock higher than desktops to the tune of 'hundreds' of MHz.