If you could find the aK (free surface area) info on them, and the ones you want to buy, that would be a beneficial comparison.
Building Physics Rule #1: Hot flows to cold.
Building Physics Rule #2: Higher air pressure moves toward lower air pressure
Building Physics Rule #3: Higher moisture concentration moves toward lower moisture concentration.
Shophound, here's a picture of the max flow registers I found at HD. There is alot more spacing when compared to the existing registers.