how tight do you put ]the bottom head?
It depends on a whole lot of stuff...
What kind of head? Kevlar or aramid fiber heads like the Remo FaLam or Evans MX5 are going to be tuned higher than a Mylar head. Those heads are designed for higher tensions than Mylar can handle. To give you at least one specific answer, Bret Kuhn answered some questions on Remo's web site when he was with the Cavaliers. He mentioned their Remo Marching Ambassador (Mylar) heads were tuned to a D and their White Max batter heads were tuned to A. And the reason I mentioned the top head leads us to the next point...
How is your top head tuned? The pitch interval between the top head and bottom head has a pretty big effect on a drum's sound. For a really obvious example, check out the toms on a drum set. The same effects apply to a marching snare, although they're far less obvious because of the drum's tight staccato sound. I seem to recall Kevin Namaky (formerly of the Glassmen &
Pearl) mentioning his preferred tuning was to go to a medium tension on the top head and tune the bottom a half-step higher.
What size drum? 13" drums will naturally have a higher pitch than 14" drums when the heads are tuned to a similar tension/feel.
Personal preference. Some people like 'em higher, some people like 'em lower. Some like their snare sound wet, others dry. The variables are pretty much infinite and there really isn't a right or wrong answer.