Mark - 2 subs in a 13 x13 room. You are my hero!

With dual subs, you'll need to deal with the nulls, but that is a small price to pay for everything else you gain (headroom, extension and smoothness).

Tak a look here at Craigsub's test results to help you out a bit. Frankly, with the subs you mentioned, you look to be in that sweetspot where you have narrowed your choices down to where you really can't make a mistake with what you buy.