bperlmu's right, wheat extract is actually a mix of wheat and barley malt extracts, already in the proportions recommended for wheat beers ( I think ~60% wheat/40% barley).
After my buddies and I brewed our first wheat (using all wheat LME and DME), we brewed a sort-of wheat beer with some left over wheat dme and regular barley dme. The beer came out much, MUCH clearer and lighter- not neccessarily a bad thing, but if you're after a nice cloudy, rich weizen flavor, not what you're shooting for.
And +1 for keeping the temps during fermentation on the lower end. Any wheat we've fermented during summerwinds up with an INTENSE banana flavor- which is again OK if that's what you're after, but when you're looking for the clovier side of weizens, the temp has got to be on the cooler side of the range.