No idea about the 40, but mine with the 25 was running a 13" Accel wasn't spectacular, but managed 21knts cruise.
I got a "portable tacho" in an ice cream tub if you want to take it for a play & experiment? (assuming it doesn't have one.....)
Also if it's a 13 spline shaft / Merc respray, you could borrow my Merc prop (14") if the spline lengths & Diameter are suitable. Also have the Suz prop, also a 13 spline, but I guess as it was OK on a 25 you might be looking for a higer pitch?