Does size matter?
 

I know that is a loaded question.....but does it? If I ferment 5 gallons or fermenting 1 gal, common sense tells me that fermentation is fermentation and will be done when it is done. But, with a smaller amount of fermentables, and the same amount of yeast pitched in each one, shouldn't fermentation complete quicker with 1 gal. vs 5?

No, it should take the same amount of time if all of the variables are the same.

In general a higher pitch rate means a shorter lag and growth phase.

In this case, most likely yes, as a significantly smaller amount of reproduction would be taking place in the 1 gallon batch. This is assuming you don't actually mean the same number of cells per unit of wort.