If they're all arriving together in one packet, I'd submit them them all. I went over the limit last year and it was fine. I could've cut out a "less important" research letter, or my non science letter, but these individuals took the time to write letters for me, so I figure I would submit them all, even if I exceeded the school's maximum.
I'm biased towards doing it this way (just b/c its what I personally did) whereas other people recommend that you should stick to the guidelines regarding number of LORs. Take what I say w/ a grain of salt.