Not a perfect analogy, but you could think of the DDR-2 rate as an army marching in cadence. At a slow funeral pace, (DDR 133 2-2-2-X ), potentially it only takes one or two steps to turn right or about face without crashing into your neighbor or getting out of line. Moving as fast as possible, double time, ( DDR-2 1200 5-5-5-X ), it might take five steps for each turn, etc to be executed correctly.
So less time spent manoeuvring ( tighter timings ) and faster pace ( higher clocks ) move the army quicker ( more data processed ) and also make mistakes more likely. And unfortunately, when you get that motherboard, memory and cpu out of the box you don't know whether they're gonna be special forces candidates or barely made it through boot camp without killing themselves. myceliv