Well right now my mag is in a 4.0 cu ft box tuned to 28 hz. Its nice and clean and gets pretty loud but I want a lil more SPL out of it. I heard if I tuned up around 35 hz it would get a lot louder but my question is how much sq will I be losing? I really dont want to lose too much sq but want it a bit louder. What do you guys suggest?? And in what kind of enclosure did you get your best results?

yeah tuning higher will make it louder. how much sq will you lose is hard to tell. You won't have quite as much low-lows, but the 40-50 hz range will be noticeably louder. If by sq you mean "tightness," well that's hard to tell. generally a higher tune makes it a little more muddy sounding, but to what extent I can't tell you. maybe it won't at all.

My 15D2 is in 3.8 tuned to 30 hz, and it's just awesome. It's the only one I've had it in, though.