On my four year old MacBook Pro - the internal temperatures and fan speeds are climbing and running it vertically rather than on a Griffin Elevator in clamshell mode. In practice, a 5 or 10 degree tilt with a minimum of one inch clearance of air under the mac gets just as much airflow and cooling as vertical as long as the air temperature isn't too hot (<85 degrees). Vertical exposes the most surface area and is best for convection moving the hot air away from the mac operating in clamshell mode.

BUT, I'd just say, the mStand looks pretty darn cool both when the mac is open and closed. Anyway, the macbook is pretty darn cool, but I'm not doing your 'close the lid while cranking the processor' plan. I own the Rain Design mStand, which holds it mostly horizontal, though angled. I know that past mac laptops (that 'killer whale' powerbook G3 I had so long ago) explicitly stated that the keyboard was one of the primary cooling elements, therefore there was no bypassing the automatic sleep-on-close. Note that I didn't even know you could keep the macbook running with the lid closed. One could guess that a truly vertical stand would only be blocking one of the thin edges of the macbook, while a horizontal one would block part of a large flat surface. Namely, 'to get your answer, you would not necessarily consider vertical versus horizontal, but simply look at the stands and see which one allows the most air to circulate, unblocked, around the macbook.' I think that in the absence of some kind of surprising physics formula, most of us would have roughly the same answer to that question.

Looks kinda strange compared to the great looking vertical stands available.

If computer sleeps, you should do the steps from 2-4 again or the internal display will be on.

Some people will not be comfortable to run their HDDs from this position (10-20 degrees vertical inclination).

You cannot use your internal IR receiver.

Better bluetooth/wifi reception because lid is not fully closed (compared to fully closed one).Takes less space than fully opened notebook.Cooler means less fan noise under load.Warm air gets up, there are no obstructions to the vents and all parts are exposed to colder air. I recommend old polyurethane mouse pad or shaped polystyrene.

Put it on the desktop in reversed 'V' form on something soft.This will force using only the external display. Connect all cables (video) and close the lid.I was planning to buy a stand (since I use my MacBook Pro with external monitor and keyboard), but inadequate cooling stops me, however keeping it open all the time accumulates dust. It's not meant to be used that way, and under full load, this probably will lead to noise and overheating. Bookarc looks great, but closing the lid means thermal problems.

Macbook pro vertical stand