At those resolutions I would recommend you pass on the 1GB 4870 and get this one:http://www.newegg.com/Product/Product.aspx?Item=N82E16814102796
This new cooling is not a gimmick. ATI is moving to this new cooling technology for all cards.
Tests show very little to no difference in all games between the 512MB and 1GB cards.
Have a look at the P5QL-E
If you are not going to overclock and not planning to crossfire, there is really no reason to take a P45 over a P43 I think. You'll get more of the features you could actually use in the P5QL-E.
If you were talking about the P5Q-E, that would be different. It's a better board all around, and only $13.00 more than the Pro.
The Zalman, or any number of coolers, are fine at stock speeds.