there are a lot of topics in this post, and i am getting in late, so sorry for jumping around -
first, CS does say that # of possessions is the primary factor in how tired a team gets. wizard, this is why an uptempo team needs more conditioning - they get more tired. not necc more tired than the other team, just more tired in general. the faq can be misleading, as most quotes by CS, unless you are very careful in reading it. another often misused quote is the one about # of possessions affecting tempo. i think it is fairly obvious a lot more is going on than just # of pos, and i have never seen anything CS said to the contrary. but, it seems many take away from CS quotes that it is just # of possessions that affects tempo. i am not sure why but am almost positive it is not true.
the uptempo issue is a very complex and misunderstood one. so many CS quotes are wrong and/or taken out of context. someone claimed uptempo did not affect fg% - this is something i've seen CS claim a couple times as well. however, i am fairly sure it is not true. i see it as two offsetting factors, 1) uptempo gets more fast break opportunities, more opportunities where the offense has the numbers. not sure how it is implemented but it seems uptempo gets more easy baskets. 2) uptempo teams try to find a shot sooner, so their shot selection in the half court is worse. my belief is in CS stat studies, they used random teams and random tempos, and saw that largely fg% and many other stats were unaffected - this is why they have claimed the only impact of tempo is on # of possessions, which is extremely misleading if not a flat out lie. i feel a similar scenario as with fg% exists with most stats, with 2 offsetting factors.
another tempo issue that people said is set in stone is, teams don't run the ball up faster. that is was not debatable. is that really the case? i remember reading a thread and thought CS said it was part of it (and at the time, i was under the impression they never said that before). anyway, Weena says the only one who can really say is TK or seble. i suggest this is a dangerous way to look at things. look at some of TKs comments on tempo, how misleading and/or wrong they have been. i think he tried to simplify things for the masses, that are grossly misleading to those who are thinking about things the most. a common theme i have observed since i started is some people put way too much stock in CS comments. and they try to build a mountain out of a molehill - CS makes a simple comment on one subject, and people pick apart the words to draw vast implications across a variety of topics. so i would like to caution against taking anything CS says as absolute truth.
finally, i agree with OR for the most part, on uptempo being mostly a disadvantage. i've long felt it was a disadvantage for me almost every time i ran it, and for almost everyone else. similarly, lostmyth's teams are the one case i cannot figure out. my theory at this point is, with a sufficient advantage, playing uptempo vs normal does not have that huge an impact. and lostmyths teams are so much better than everybody else's, that he is going to win those regardless. but the close games, i am somewhat convinced uptempo is a serious disadvantage. at the very least, when i have the best team in the country, i am 99% sure that any team running uptempo is shooting themselves in the foot, badly. on the order of halving their chance of winning. i think question of "is uptempo useful" is totally different when you are talking about playing a significantly worse, roughly even, or significantly better team. i think the value of uptempo is roughly on a sliding scale, where it is questionably useful at the bottom end (playing a worse team), and a crippling disadvantage at the top end (playing a better team).
that said, i think the type of team matters as well. i play a guard sf, with intense focus on speed at the 1-3. i think this is the worst case scenario opponent for somebody playing uptempo. so i think this skews my point of observation badly. i am virtually positive nobody should run uptempo against me when i have one of my better teams, i have watched that extremely closely and have a pretty big sample size. but that certainly doesn't imply anything for other teams, even other really good teams.