When selecting a material for a large floor area (48'x48'), what material is best for conditions with some variation in temperature, say between 50 degrees and 90 degrees. I was told by a salesman that laminate is not good for much variation in temperature. However, an article I read on-line indicated that a properly installed laminate would make allowances for expansion and contraction of the material. What about hardwood and does it matter whether it is pre-finished (and beveled) or unfinished wood to be finished after installation. Another source implied that the unfinished hardwood that is finished after installation does not do as well with temperature extremes as the pre-finished hardwood with beveled edges. Any and all guidance would be greatly appreciated.

Wood is more effected by humidity, but temperature plays an important roll, in humidity.

Engineered Teak, but have a pro install it for best results.

http://www.flickr.com/photos/13772863@N08/3398924069/

Site-finished , factory finished, beveled edges...... none of that really matters. Same rules apply as to controlling temp and RH. What is the humidity range?

There's a reason this wood has been the most sought after by the marine and furniture industry for eons. Called the King of Woods its dimensional stability is superior to most hardwoods. Soak it in water, then bake it in the sun it dont change much dimensionally or split either. To bad its been harvested to death, but then there is the reason.

Since your question relates only to wood's stability, without any other considerations; the top three domestic woods are : Black Cherry, American Walnut, and Red Alder.
There is no perfect wood, you must list all the factors required for this floor and select the one that is MOST suitable.
Consider: stability, visual appeal, durability, surrounding decor, etc.

I'd call Texas Mesquite, Domestic. About the most stable wood, besides real Teak. Stuff grows like bamboo around here, once established. Can't seem to kill it.

Yup, Arizona mesquite is better though.

Not much wood harder than mesquite besides Ironwood.

Agreed, about the stability of Mesquite. However, it is a look that would have to "grow" on you. A lot of people find it too visually vibrant.
Personally I like it, but a lot of people do not, which is why I didnt include it in my list.

Isn't engineered flooring more stable than solid flooring?

I know maple isn't the most stable of woods, but when it is the top layer of an engineered floor, doesn't that make it more stable?

Although engineered flooring is more stable than solid, it is not inert. After all, it is still wood.
I think i would refer to maple engineered as less unstable, lol

The majority of what is out there today is not true engineered wood.

True engineered wood, has an uneven amount of plies.
The thickness of the plies are equal.
The top ply and the bottom ply, both go the same grain direction.

The plies are of the same species of wood.

What you see today, is a thick sawn species of wood your buying, but under that is a variety of different species. They are milled much thinner then the thicker top wear layer. Each species of wood has a different shrink and swell ratio, so things get real interesting when there is high humidity and low humidity. Manufacturers call it "shear" LOL No it is a board manufactured to fail, when sold and marketed as an engineered, "It is more stable then solid" Wrong!!!! It acts just like a solid.

Then on top of that, some manufacturers got the bright idea, to make even number of plies. The bottom ply is going the opposite of the top in grain direction. Ya that's "balanced", Wrong! Instead of making a complete board at one time, They are using already constructed plywood. Cutting it short rip across the grain, then gluing the thick sawn board to the top. Here is where the board wants to cup, and delaminate, Something you very rarely saw, 10 years ago, when the boards were the same species throughout the plies, and equal thickness of the plies.
Heck, the old 3 ply sold 10-15 years ago, holds up well in Arizona, and out on the pier over the water.