That is like a $600 retail sub. Of course the DIY of similar price will outperform it considerably. But I would expect your DIY sub to sound better than even most $1500 retail subs, assuming you have the plate amp controls set properly.
Take a chunk of soft cushion foam and secure it in some way so that it is positioned exactly where if the cone moves out 30mm, it will touch the foam. (Get out your metric ruler.
)Now play the movies at the SPLs you desire and see if the cone is touching the foam when in use. If it is not rubbing/touching the foam, you'll be fine. I expect that you will not be touching the foam.
-Chris