From what I've read all over the place, is the reason 1:1 is used is so that you can get your highest FSB clock speeds without the memory coming into play (for stability) because of the lower divider (frequency) used.
Now, IF I had a better CPU cooler and was going to go up to 3.6Ghz or higher I'd use a lower memory divider so that my memory wouldn't be so overclocked that it couldn't keep up anymore.
This is the reason I now have my memory at 4:5 (667) to keep it around 800Mhz which it is designed to run at and is stable, not to mention I found no benefit (added throughput) to overclocking my memory to 960Mhz. But I did notice much better throughput once my FSB went up & my games played much smoother.
That's my take on it anyways...Correct me if I'm wrong though guys! hehe
Btw, just so I could see I did a little experiment & I put my system back to default and played some of my games at their current "high" settings to visually see if there was any noticeable difference...
OMG!!! Jerky, lag and slow to catch up in places with stops and starts... What a diff without the added throughput!!!