Misconception. DDR3 is just DDR2 at higher speeds. I know this sounds just like what you said, but let me give you an example. DDR goes as high as 1333MHz I think. DDR3 goes as high as 2000MHz from 1066Mhz (maybe the lower end is higher). DRR3 @ 1333MHz = DDR2 @ 1333Mhz. So no difference in speed, at same speeds. Does that make sense? And because Intel's CPUs only go as high as 1333MHz (may be 1600MHz) you can only use a max of 667MHz (or 800MHz if CPU @ 1600MHz) of RAM tops. If you buy anything higher it will bottleneck. However, I'm not sure on this number for AMDs. I still need someone to explain that to me. Can RAM use all of the listed frequency on a 2600MHz HTT or is it half? Overall, DDR3 is a waste (for Intel's) until the Nehalems come out.
What about the difference in bus speeds of DDr2 and 3? That'll make a difference. so no, NOT the same speeds. It's like saying DDR - 400 and DDR2 -400 is the same speed, and anyone who's used both will tell you it's not. It's like saying a 3.0GHZ processor on a 533 FSB (if we go back to P4 days) will run at the same speed as a 3.0GHz proc on a 800 FSB.
And anything beyond CPU clock isn't always overkill as you can change the ratio to get better rates.