I give mine a lil over 400 and they take that power like a champ. But if u were going sealed i think 1.25 might be a lil big. Alpine's web page says .7 to 1 cubic feet for a sealed enclosure. Dont know if they wont sound good with 1.25 cubes im just tellin u what alpine says
I would put them in no more then 1cb.ft. sealed box... as far as the power goes in a sealed box 500WRMS would be just fine, they'll even take 600-650 each sealed in the recommended enclosure. For SPL use I remember this guy running 1000WRMS per sub, and they did just fine. It's mostly all in the install.