IMO, the stock AMD cooler is adequte enough for light overclocking. Anywho, I've heard a lot of great things about Gigabytes mobos. Lately, they've been targeting the OCer croud, and they have th products to back it up.
Depending on what you use it for, you should see somewhat of a difference. If you game, you probably will. My question is, what kind of memory do you have and what kind of PSU do you have? You do realize that the motherboard your looking at requires DDR2, right?