I don't see how prop ventilation would change if the prop were changed from 3 to 4 blades assuming of course that the diameters were the same. Your ventilation sounds like a trim issue, ether the tabs of the motors or both.
I can see a situation where the extra thrust that a 4 blader would have over a 3 blader at certain speeds could make a difference but only to the extent that is offers more 'push' as the hull rides ( breaks) the swells. So if your boat currently slows when it hits the swells, more oomph could help. The hull trim and angle of attack have a lot more to do with bow steer.
I told Ken that my motor sits a little low so naturally wanted something with stern lift. My other requirement was lower planning speed. Huge difference. The four blade really lifts the stern out of the water. The wake it produces it totally different. I was having a hard time staying on plane under 21 mph. Now I can plane easily at 17 mph. Mid range is better gets on plane quicker really better at every rpm.
Top speed is about the same. Two negatives, one is I now have a little bow steer until I get the boat trimmed properly didn't have that before. Second negative is a little prop chatter??? At idle speed there is some vibration that wasn't there before but can be somewhat alleviated by either trimming motor all the way down or trimming up.