I can't really comment on the motherboards, but it seems these days all but the very cheapest motherboards have at least a few overclocking options. You'll have to ask the Motherboards forum here for specifics.
As for which one is faster at a given clock speed, that would be the E5200. The Core 2 Duo is faster, clock for clock, than the Phenom I. So if you compare a dual-core Phenom @ 3.2 vs. a dual-core Core 2 @ 3.2, the Core 2 will win.
Also, the E5200 should be cooler. It draws significantly less power. You can see why the E5200 is so highly recommended. The next best step up is probably the Phenom II X3 710 or 720, but they are significantly more expensive.