Should have asked here first! Please help!

Well, the long and the short of it is, after a lot of painful searching, research (apparantly), and trying to get everything perfect, I ordered my new PC. The core 3 items around it are:

An E6600, Gigabyte P965 DQ6 and 2x1GB Corsair DDR2 Value Select PC5300 Dual Channel Kit with CL3. Not only do I intend to do everyday work with this machine but intend also to hammer the heck out of it, playing new games and doing DVD encoding or something, just because I now can.

My big problem is the memory, which may or may not be supported by the board. Furthermore, I get this horrible feeling that although Anandtech shows this memory running at (2:3) - 800 DDR2, 4-3-3-8 @ 2.2V. That I may have made a big mistake not going for something like the XMS2-6400 CL4.

What I really need to know is, from the memory people (who I should have asked first), when all my bits arrive in the post tomorow, should I be sending the memory back as soon as possible? How much of a performance hit do you get from using cheaper 667MHz memory? Will I even notice the difference? How could I tell if the memory was such a bottleneck? Many reports in the CPU forum have indicated that DDR2 memory at higher speeds do not make much of a difference with Conroe.

Adding to all this, I'm hardly an extreme gamer, 30FPS is high and completely smooth to me. And I have been used to a P4 1.6GHz now for 4 years. Even though this is going to be a huge leap, I dont want to have wounded the PC before it even gets going.

Am I just an unlucky fool who didn't do her research properly? Or has blind luck meant I will be completely happy with the build? If I try it and see, how can I find out if the memory is a bottleneck? Any help and advice (no flames) would be really well appreciated. Worst comes to the worst, my budget can stretch about another £50 on memory or so if I go without food for a week.