Very nearly perfect match. Same construction, same drivers, different grill, recessed tweeters. The only difference SHOULD be a bit wider of a sweet spot. It would probably be a slightly better match than your 40's, although really I'd just stick with those unless you have some good reason to upgrade. Surround speakers just plain don't do enough work to justify having a $500, 100+ lb. speaker in that position. Doesn't hurt, of course, but it's unlikely you'd notice any improvement going to the (slightly) larger surrounds. IMHO.