Bryston 3B cubed or 4B cubed?

Hello. I want a Bryston to power Focal 1038Be in a room 16 x 26. Mainly acoustic music, Folk, Jazz, World, moderate or less volume.  The system will be a Lavry DA10 DAC directly into the Bryston. I will make my own cables with Mogami as usual.
 I have to believe that the 3B cubed is enough amp for my application, however I wonder what differences I might experience with the 4B cubed in terms of soundstage, depth, 3D realism, etc. 
 Any input appreciated.
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Focal/Jm Lab speakers are very good indeed. Regarding the 1038Be take caution with selected gear, as the Be tweeter, can get bright or hot easily. A power amp with a touch of warmth is the one to purchase.
Have fun shopping around and keep us posted.
I am in the process of scheduling an audition with the 4B3 amp very soon.

Happy Listening!