New water pump 6 impellers whats up with that!

I took some pics and measurements on the 2 new pumps I have. One is a 6 blade and the other a 8 blade. Here's what I saw

Impeller size 8- blade 3.59" dia x.71"high.....6-blade 3.85 dia"x.82" high

Using a straight edge I measured the amount the impeller sticks out the back of the pump casting. The 8 blade sticks out .080" and the 6 blade sticks out .23". HUGE difference but you'll notice in the pics that it looks like they got a little crazy pressing the 8 blade impeller on which made it worse. Yet at the same time if it weren't pressed on so far there would have been a much larger gap between the impeller fins and water pump cavity. Speaking of the fin to water pump cavity distance, I forgot to measure it but they look very similar. My car is put together and I don't have an extra timing cover to see how deep the cavity is but I'm sure the 8 blade won't even hardly protrude into it because of the thickness of the gasket. I would think due to that the 8 blade pump wouldn't cool very good.

I also did my best to measure the cavity diameter and depth in front of the impeller. The diameter on both was 3.0" but the 8 blade pump has a much shallower cavity at 2.25" vs. 2.88" for the 6 blade. I'm not sure what effect this would have on things???

Not only did the 6 blade pump have a larger diameter impeller but the milled area in the pump where it spins is slightly smaller than on the 8 blade pump so there is much less gap around the impeller fins to the pump casting.

Based on what I see my 6 blade pump would pump more water even in spite of it having 2 less fins.

One last thing, the 8 blade pump has a much larger diameter front bearing making it appear heavier duty. Probably due to the factory spinning it faster. The rear bearings look the same but it was impossible to get into them to measure them to verify that.