memory - How do calculate which RAM option would be faster?

I've been reading DDR and related info on wikipedia but am still not sure I know anything.

I have a Fujitsu Celsius w340 workstation with the following:

• Memory Speed: 533 MHz


• Memory Specification Compliance: PC2-4300


• Dual Channel


• Configuration Features: 2 x 512 MB

I have 2 x 512MB PC2-3200 sticks (which is what it came with) and I have a stick of 2GB PC2-6400.

Now I've replaced the two sticks with the one so that I have 2GB to run windows 7 and there's not really a problem. But in future I would like to know what I'm doing so I have to ask and can't figure it out.

Which is faster?

There doesn't seem to be any information on what "Memory Specification Compliance" is.

I also can't figure out if "Memory Speed" is the memory clock or the I/O bus clock, and I would be lying if I said I know exactly what either of those are. Is the I/O clock the FSB and is that what "Memory Speed" of the motherboard referring to?

And does the fact that my Windows7 installation is 32bit matter?

I know the PC2-6400 is theoretically twice as fast as PC2-3200 but would the 6400 be operating at it's full potential or would the advantage of Dual Channel on the two 3200 sticks outperform it?