I think the question was less about what we know versus what we think..
I think it depends on the locale. Acclimation is a two-way street. Elevation and climate affect games. At the same time, do not under-estimate the effects of down-time on players. A few hours of leisure per day in a place like SD may, MAY, have detrimental effects on the effectiveness of some players.
Personally, I think a team should acclimate as soon as possible. A billion dollar organization has the resources to isolate 75-125 people (coaches, players, etc). People as a rule are affected by geographically measurable changes, in all regards, particularly finely tuned machines used to regiment. Anybody who is a car nut will know their sports car bought at low humidity high altitude conditions performs differently in other conditions. Add the human condition and it multiplies. The gamble lies in whether or not it matters.
Get the boys used to the environment. Turn it into mere background rather than a distractionable factor.