I went from a stock windshield to a 25" (plus 2" wider) windshield and I sure can tell the difference at 65-70 MPH.  Getting pushed around a bit.

What brand?

ClearView

I put a Rifle on mine and it made a big difference. 

I  have a Cee Baileys. It was on  the bike when I bought it. I would like to get one that is at least a couple of inches taller. I  think mine is about 25".

I went from a stock windshield to a 25" (plus 2" wider) windshield and I sure can tell the difference at 65-70 MPH.  Getting pushed around a bit.

  Does it have a vent? getting some air helps.

Yes, the vents open.

I had several heights of windshields, from the tallest/widest vented C Bailey to some that I cut down almost to the mirror mounts.   On the short ones the wind moves the rider around, especially if you wear a 2XL full face helmet and have a size 54 chest.   On the tall ones the wind moves the bike around.   At speed, I felt that the side scoops really make the bike run areodynamically dirty, But in the Texas heat, your legs get hotter than a brisket in a smoker without them.   

Seems I get less of the "pushing around" factor from the wind with the Rifle w/s than the Cee Bailey.

I  have a Cee Baileys. It was on  the bike when I bought it. I would like to get one that is at least a couple of inches taller. I  think mine is about 25".

I bought a 26.5 Cee Bailey to replace a broken Rifle.  Then I replaced the 26.5 CB with a 25.5 CB for better visibility.  26.5 is as tall as Cee Bailey's go for the C-10 I believe.

There is a corner of my 26.5 CB that cracked when i overtightened it. Superglue and vent tape can hold it together but I wanted to see over it a bit more.  Both the 26.5 and the 25.5 do fine for wind deflection for me.

Both of my CB windshields have NACA vents cut in them.

If you want to try the 26.5 CB, I'd part with it for a six pack of Root Beer and $100 shipping and handling.  :-)