yeah, since 2000MHZ means each clock cycle goes 2000/800=2.5 times as fast as at 800MHZ, hence the same amount of time goes by with 10 clock cycles at 2000MHZ, as with 4 clock cycles at 800MHZ
I can't see a quick adoption to DDR3 at this point. The numbers I've seen aren't very impressive, might be due to young chipsets, "P35 chipset", but non- the less the cost of DDR3 will be pretty high.
Not to mention that DDR2 is drastically coming down in price.