I'm not sure where the 3:4 is in the P4B.. Thugs? It is a tradeoff of FSB/CPU speed VS mem speed. If you get up there in FSB speed, you will be running 1:1 anyway since the ram would not be able to handle 3:4. Here are examples.
133 FSB, 2.128 GHz, 1:1, DDR266
132 FSB, 2.112 Ghz, 3:4, DDR352
In this case, the setup running DDR352 would be faster
You are now running:
156 FSB, 2.496 GHz, 1:1, DDR312, which is not bad either. Since you can't use 3:4 above 132 FSB, there is no decision to be made in which way to go.