Can the 13ʺ MacBook Pro satisfactorily drive two Thunderbolt displays? The new 13ʺ Retina MacBook Pros have 2 Thunderbolt ports, and Apple appears to indicate you can plug in and use 2 Thunderbolt displays with them, but is the video performance satisfactory when doing so? I'm not planning on doing anything that graphically intensive, but I wanted to make sure that the performance was still fine. (Also, I'll be using the MBP in clamshell mode, so I'll only be driving 2 TB displays, not 2 TB displays and the laptop screen.)
Yes - the CPU/GPU are powered up enough for two external screens in my experience.

My experience is Apple won't bless as supported configurations where the majority of users will see laggy performance that cannot be tuned if needed with a firmware update or better drivers.

The higher end 15 inch retina MBP can crank out many more pixels, but the situation you mention with two TB displays with the Mac operating in closed-clamshell mode actually is less pixels to drive than the situation of one display and the internal display still running.