I have a Fountain 24CS with a 502. Boat currently has a 24", 4 blade Bravo I Prop and turns 5000 RPM at 70 MPH dead on.
the previous owner had a box of parts he sold with the boat and in it was a 26", 4 blade Hydromotive Quad IV. I am wondering what difference i would notice before i go through the trouble of pulling the boat out of the water and swapping out?

Im thinking probably a few more MPH at top end but it would have a worse hole shot? Any thoughts would be appreciated. Thanks.

your 24 bravo is equivalent to a 23p hydro. Unless it has been labbed, your Hydro will spin at about 4400 max. hard to say where your top speed will be though.
Carder

An inch of pitch is only a 200 rpm drop.

The boat will run flatter with more stern lift. This is of course if the props are stock. The Bravo will often get on plane easier and have a better ride at WOT.