Yeah, saw crucial says DDR for 700 and DDR2 for 6000, but also noted it only says upto 400Mhz DDR2 for the 6000. Guessing that's because the std 6000 config comes with 400MHz FSB, because otherwise the $50 upgrade to 533MHz is pointless.
Wondering though about the backward compatibility of DDR2 and inter-operability with DDR.
Regarding the coupon, it does stack, but hoping someone says it worked for them with a non-Discover card.