It really does not matter. 1:1 ensures stability but if you run other ratios, no matter.
If your CPU FSB is 375, running a 1:1 ratio, that will set your RAM to 375 (750 rated). There is nothing wrong with that setting as you'll not see a difference if you were running your RAM @ 533 (1066 rated)
There is no way you will be able to bring the FSB of that CPU to 533 so don't even try it, the highest you'll get is likely 425-ish but there's no point.
Since your RAM is technically underclocked when using the 1:1 ratio, you might try to bring yout timings from 5-5-5-15 to 4-4-4-12 or something, this will yield a slight improvement if successful.
Thanks for a stellar answer