I had the 7nm with my unmodded D10 and was not happy with it, I sold it !
Now I have a modified D40 and want an H Alpha filter again.
The 7 nm took long exposure times before getting any results. I would try a 12nm or 13 nm again before buying a 7nm.
I'm not an expert in the H alpha field !, but I did see a lots of great results taken with DSLR's and 13 nm H Alpha filters.
Just my two pennies here.
I'll try to dig out some webpages. I saved a bunch of websites about DSLR and H Alpha, but my computer crashed and all the information was gone. I think if you google DSLR and H Alpha you're getting close.