OK you got the NT Zalman, four pin, so all is good
Ram timings are the speeds, to get your ram operating in dual channel you'll need both sets running at the same timings, tighter timings (lower numbers) = faster data transfer, you mention 8500 again??? I thought you said all four sticks were 6400???
Anyway, you'll need to adjust the timings so all four sticks are running the same, you do this in the bios once you have the pc assembled.