It's correct: even with bad timings DDR2-800 works faster than DDR2-600 with the best timings. DDR2-1000 is only a little faster than DDR2-800, the timings being the same. This looks like a convincing illustration of the fact that it's unreasonable to use memory with a resulting (DDR) frequency two times that of the FSB clock rate.
Although PCMark05 isn't very sensitive to memory subsystem performance, it still gives us some basic trends. DDR2-800 enjoys a bigger advantage over DDR2-600 SDRAM than in the tests with a non-overclocked CPU. The DDR2-1000 configurations turn to be slower than the DDR2-800 system that allows using the aggressive timings of 3-3-3-10. Well, even if you compare the results of DDR2-800 and DDR2-1000 with identical timings, you will see that the faster memory only scores a few extra points in PCMark05.
The same can be said about the results the memory configurations showed in the complex memory subsystem benchmark from PCMark05.
3DMark06 results don't depend much on the memory subsystem speed, so there is not much matter for us to discuss here. You should be aware that higher memory performance doesn't necessarily lead to a big practical effect. There are quite a lot of real-life applications that do not work with large amounts of data and thus do not actually need fast memory. So, before purchasing fast overclocker-friendly DDR2 SDRAM modules, you should make sure you do need them for the applications you are going to run on your computer.