Paul, I would guess that it would depend on how strong you are and how your muscles fare with multiple accelerations. For instance, sprinting to catch waves over and over again might even be easier when using "a smaller gear" like a smaller paddle blade for some paddlers. Others, maybe with a high power to weight ratio or with a natural sprinting ability, might do better with a larger blade, like you ask. It also depends on how good a downwind paddler one is because while the elite guys are sprinting at 8-12+ mph and might get along well with a larger blade (though most use medium size blades), the average downwind paddler might be sprinting repeatedly in the 7-9 mph range, and be better off with their normal size blade.
I guess you could think of a similar analogy using a fixed or single speed gear on a bike - with the caveat that you would use that one gear on undulating terrain.
The same argument holds true with longer vs shorter paddle lengths, too, in my opinion.
I've tried a larger blade and a longer blade on a downwind before and it wears me out much too quickly and I end up slower. Erik