Even a 2-3 degree drop in mash temp will make a massive difference to attenuation. You'll be surprised.
Worry about amount of crystal for taste reasons, worry about mash temp and healthy yeast for attenuation. In my opinion.
Only 2 beers?? Good god you've gotta be kidding me, there's way too many beers out there to limit yourself to just 2, I like to go through 3 or 4 different beers in one night let alone a whole year!! haha
Lowering the crystal from 13% and mashing a bit lower would definitely help to lower sweetness. Using darker crystal may also help. Otherwise, I haven't got a lot of experience with Foreign Extra Stouts...
Two beers till I get them right ... every beer I've brewed has been different. They've been OK, but all need improving ... rather have two good ones than 10 mediocre ones.
Of course I do plan on brewing for a good few years yet, so I can see twenty or thirty really good beers in my future (if my liver lasts that long).
Belgian Ardennes Yeast pitched @ 26 capped @ 29 degrees
Cripes! Have you fermented that profile before?
Are you expecting bananas & nailpolish remover or just intense Belgian Phenolics?