I've got a 9A with an IO-360 so my numbers will be slightly different than yours but...
I started with a 3 bladed Catto prop just as you described. I loved that prop and it performed better than any certified airplane I ever flew (granted thats not a long list). However last year I got the bug to go constant speed so I installed a Whirlwind 200RV prop. You can read all about my thoughts on the process on my
blog.
Here are the high points.
1. Cruise is no better with the constant speed..in fact its slower but only by a knot or two. To be fair to the Whirlwind, it is limited to 2700 rpm so I have my governor set so that I can't get above 2650 in cruise. The Catto would turn at 2750 which means I was getting more HP out of the engine.
2. Climb...holy **** the climb! The constant speed out-climbs the fixed pitch by a large margin...and thats saying something because the Catto would climb at 1500+ fpm.
3. The constant speed prop is quieter in cruise because I can pull the engine rpm back.
4. The ability to slow down with the constant speed prop is great but the con to that is my glide ratio really sucks now. In my informal testing I could glide at >10/1 with the Catto at idle but with the constant speed at idle that number drops to about 8/1.
5. The constant speed prop is has much more vibration than the 3 blade Catto. I even dynamically balanced my prop to 0.0 IPS and still have much more vibration. I've gotten used to it but that took a bit of time.
Was the conversion worth the money I paid? In
my opinion the answer is no. The Catto is that good.