Budget E2180 build questions

[initialised]

I'm building two near identical systems on a low budget, aiming to keep below £150 (~$300) per system. Both the systems are CPU/Mobo/RAM upgrades of SoA Athlon based systems and will be primarily Office/Internet PCs rather than gaming rigs so onboard GPU is fine.

I've settled on the E2180 (£54) as the CPU and 2GB (2x1GB) Corsair TwinX XMS2, DDR2 PC2-6400 (800) 4-4-4-12 (£36)for the memory. Any better options?

What OC can I expect from the E2180 on the stock cooler?

Would it be worth trading off an E2140 (£42)/E2160 (£48) against a better cooler (Arctic Cooling Freezer 7 Pro £13) to acheive a higher OC? I am not 100% sure this will fit in one of the cases.

How likely is it that I'll need new PSUs, if so what wattage?

And most importantly, which motherboard to get?
I'm currently looking at the Asus P5KPL-VM, iG31 uATX, On Board VGA. On board graphics is preferred but I would be willing to trade this off for a higher CPU OC and a ATI 2400/NV 8400 so long as I can stay in budget.

[Yamcha]

I would go for E2140 or E2160, from what I've seen they tend to do better then E2180.. i've got a E2160 L2 @ 3.2Ghz, I can get it at 3.3GHZ without going over 1.5V