The EP 45 UD3R is a very good board an an excellent overclocker. I ran an E8400 at 4Ghz for several years on one with 4GB od Corsair DDR2 800. P45 was in my opinion the very best LGA 775 chipset.
That being said a Q6600 will top out at 3.4-3.6Ghz with good cooling ( a Hyper 212 is sufficient ). The Asus board with the G41 will almost certainly get you to 3Ghz if not higher. Since it's obsolete tech I would spend as little as you can so the $25 option seems best.
The Core2 chips work best at a 1:1 FSB to RAM ratio so DDR3 is not necessary.