What's the Best Frequency Ratio between CPU & RAM?

What's the most ideal frequency ratio between the CPU and RAM? What kind of theory is this based on(if you know)? In addition, does a 3GHz dual core CPU give better performance than a 2.66GHz quad core one in most case? Lastly, how do you choose motherboard? (e.g. Would you choose ASUS P5Q-E or ASUS P5KPL? why? ) Thanks a lot!

Sorry for not describing my question clearly! Here's my new description.

1) The best CPU & memory ratio for FSB 4.8 GT/s, 1333MHz, 1066MHz & 800MHz?

2) I mean the performance between Core i7-920/Q9550 and E8400?

3) Which M/B should I get if I am not an overclocker? P5Q-E or P5KPL?

Thanks mate!

1)for the i7 there is no best ratio, for core 2 and below the best is 1:1

2) the e8400 and i7 920 should be pretty even in todays apps because the i7 has a higher IPC, but the i7 will win in apps which use more than 2 threads,and the Q9550 will be in between the two in those apps but below both in <2 threaded apps.

3) the i7 doesn't work in either of those boards as it uses the 1366 socket where motherboards are a good deal more expensive. but for the core 2 line, the P5Q-E is a far better choice.

Thanks for the answers, guys!!!