On asus P45 boards you can only use PL7 on the 3:4 and lower divider, meaning at 500FSB your ram would be at 666 MHz. P45 is not P35, you can't say because your P35 does a certain PL at a given FSB/divider a P45 can.

On a UD3P you should be able to set PL7 on say 4:5 or maybe even 5:6 (they can run PL8 on 1:1) but it would take more vNB to do it, and the performance on the UD3P's from what Ive seen is about one PL higher than Asus boards, such that Asus PL8 = Giga PL9.