Well I managed to achieve a 1:1 ratio by accident, with my FSB @ 378.
I overclocked to 3.4ghz and the only memory option that didn't overclock it(2x), gave me the 1:1 ratio
Granted this is on a P35-DS3L. with everything @ stock/default its a 4:5 ratio (with my E3110/8400 anyway)