The CLA has a completely useless backseat...it might as well be a coupe. If you are over 5'2", it is tough to get in the back at all.
As for engines, the April 2014 Car and Driver has a short article (page 58, but not online) on the 2015 A4 and upcoming S4. It says the S4 will have a supercharged V-6 (sound familiar?). Hopefully with even more HP.
As a side note, I am still not sure the C63 is really a direct competitor of the S4...probably a better competitor the the RS4 (that isn't sold here). The C63 for sales at my local MB dealer stickers for $93K...and it wasn't a black series! Yikes!
2011 S4 Brilliant Red, Red/Blk leather, 6MT, Sport Diff, Navi, 19" wheels, Carbon Inlays, supercharged badging, 3M clear bra, 35% tint, 18" tires/rims for winter, etc.