There are various opinions about this.
My personal opinion regarding CPU-to-RAM dividers other than 1:1 is that they introduce wait-states into the transfer of data between the two components.
Some here -- including (I think his handle is "Graysky") the OP of the sticky on over-clocking C2D and C2Q processors -- argue that 1:1 gives the best performance, and that any improvements in other ratio choices only show in synthetic benchmarks, and not real-world performance.
A lot of noobies to over-clocking, and people too timid to get their feet very wet with it, shy away from tweaking the memory timings (or latencies). There is a very good article at Tom's Hardware published between 2003 and 2004 about tweaking the latencies, and it explains the contribution of each timing to the performance of any, single memory operation. For instance, the lower the CAS (column-access strobe), the faster the memory operation. But also, the RAS precharge delay, as I understand it, affects the overall length in clock-cycles of the memory operation. Obviously, various active processes or programs on your computer will execute thousands of those operations in the blink of an eye, but the tighter (smaller or lower) these latencies are, they will affect proportionately the time it takes to perform completely any given task involving memory.
So tighter latencies mean faster speed without stressing the system with higher frequency -- clock-cycles per second in megahertz. Instead, you have reduced the number of clock-cycles at any given megahertz setting to perform an operation in memory.
In the past, some memory manufacturers who produced high-performance (high megahertz) memory created products that were not downwardly flexible in the latency settings. For instance, this was my experience with OCZ Gold EL DDR-500 and OCZ Platinum XTC EL DDR-500 modules: you could not run these modules at DDR-400 and expect to set the latencies at lower than the stock DDR-500 settings. Other modules of both DDR and DDR2 vintage proved to be very elastic. For instance, I could get OCZ Platinum DDR-400 modules with Aeneon chips on them, and the stock latencies at 400 Mhz of 2,3,2,5 were very stable up to 454 Mhz without pushing the VDIMM voltage to the warranty limit. And DDR2 modules with Micron D9 parts have proven to be very "downwardly" elastic in the high-performance flavors -- for instance, my Crucial Ballistix (Micron) DDR2-1000 modules have SPD settings of 5,5,5,15 for the rated 1000 Mhz speed, but I can run them at 3,3,3,6 at DDR2-667, and 3,4,4,8 at DDR2-712.
I get some very good synthetic benchmarks this way with Everest Ultimate, and I don't have to stress the motherboard more to break even with higher Mhz settings.