So why not have a prop shop put some pitch into the metal prop? That usually costs around $100 if you aren't asking for paperwork and log book entries.
FWIW, I find about 150 RPM difference in my planes (one slow plane and one fast plane) between operating from airports at 7000' vs airports at sea level (I am based at over 7000'). That can be made up by a pitch change of roughly 4". A pitch change of 20" is huge. They do measure them differently from manufacturer to manufacturer, but I have flown behind Sterba props before and his pitch measurements aren't that different from the rest of the world. On the other hand, Ed has been in the business a long time and will work with you to get the prop right for your plane.
FWIW, based on my experience with a number props from a number of manufacturers on various planes and engines over the years, I'm guessing the 60x60 will have a bit more bite than desirable for an A-65 on a Sonerii, but should be close. It would be a lot closer than a 40" pitched prop. I suspect the 40" number may have been misread or otherwise incorrect (as in the prop was repitched, but not restamped) That's significantly less bite than you'll find on a 75 mph Cub with an A-65, typically swinging a 68x44 prop.
As for effects on the plane? Metal props generally turn smoother due to the weight acting like a fly wheel. But the wood prop is smoother in that it doesn't have any harmonics. If you hit the prop it just shatters, so you don't need to tear your engine down. Sterba uses a tough polyurethane leading edge that will protect the prop from rocks and rain damage, but keep it varnished to protect while sitting. The airfoil on a wood prop is typically thicker, so isn't as efficient as a metal prop. However, Sterba has been working with the KR crowd for a long time and has his props dialed in nicely for planes in that class.
The #1 thing it will affect is your W&B. Make sure you check it.
-CubBuilder