Carl is right. For performance in any phase of flight, you can’t beat a blended airfoil Hartzell. It will give you cruise efficiency that you can’t duplicate in most scenarios with a fixed pitch prop, and will at least equal, or almost equal any fixed pitch prop in climb, and will allow you amazing descent angles for tight approaches that a fixed pitch can’t do. This level of performance requires money, as well as loss of payload, compared to most competitive fixed pitch alternatives. For the OP, you’ve said that you are interested in flight mission profiles that for the most part are local in nature. I have the same mission with my RV4. I can’t say enough for keeping the weight off, especially for local fun flying. I could get a little better cruise efficiency with a constant speed prop, but to do so would require spending $10K more than I did with my GA Sensenich, and I would have to remove my O-360 engine from my airplane to modify my firewall to accommodate the required prop governor. You won’t have to do that joyful exercise with your RV8, but the money and loss of payload is for everyone contemplating this option.
My original prop on my 180hp RV4 was a Sensenich metal 72X85 prop. That prop would overspeed my engine at WOT at any altitude - 2900 RPM. In order to respect my engine manufacturers limitations, I couldn’t get more than 60-65% power without over-speeding my engine, unless I was at a relatively high altitude, >8K’. My new GA Sensenich will now not exceed 2700 RPM at WOT and I am able to run my engine at a more comfortable 65-70% power at any altitude - up to a point - without exceeding my 2700 RPM limit, and at a higher MP (% power) than I could before. I have my pitch set to not exceed 2700 RPM, and that setting has resulted in a degradation of enroute climb performance by a little, but it is still pretty good - 1300- 1400 fpm at 125-135 KIAS normally, so I’m quite happy with that. What has surprised me is the takeoff runway performance with my new GA prop. My runway performance has improved by about 20-25%. Even though my pitch setting is more aggressive, my static RPM is about 200-250 RPM higher at the beginning of my takeoff roll than with the metal prop, and I get off the ground about 100-150’ shorter. The carbon fiber, scimitar shaped blades of this prop flex forward slightly (so I am told) at takeoff power - high torque/low or no speed - and because of the scimitar shape there is a change in pitch in the curved section of the prop, and results in a slightly higher RPM (about 2270) - sort of a quasi constant speed. This phenomenon (if true) is born out in RPM indications during takeoff. I notice a reduction in WOT takeoff power RPM after accelerating through approximately 70K+ to about 2150, where it stays until I accelerate above about 100K.
My original metal Sensenich prop would outclimb every Hartzell propped RV8 that I fly formation with - at a noticeable margin, but I was climbing at WOT and 2600 RPM/130 KIAS. My pitch attitude determined my RPM at WOT (still does), and if I wanted to climb at 2500 RPM instead, I would see 2500+ fpm. That prop is for sale, BTW, if you’re interested. I would recommend the Sensenich GA carbon fiber prop for your RV8, if your mission profile is mostly local flying and acro. If you are planning a lot of cross-country, especially long distance, then you might be able to justify a constant speed, but don’t expect to pay for the difference with fuel savings. That Hartzell, or Whirlwind will give you a comfortable cruise, no question, and it will increase your resale value too. I have owned 5 RV’s, 3 of which I built and had CS props on all 3 - 2 Whirlwind 200Rv’s, and a Hartzell on the third. My first RV4 (purchased) had a Catto 2-blade and it was a beauty, but it turned the engine at 3000RPM at WOT, even at 11,000’. I had Mr. Catto adjust it, and he was able to reduce the max RPM to 2900, but I was still leaving performance on the table if I respected the Lycoming limit. On this, my hopefully last RV, I decided to go with the Sensenich GA. For lighter weight fun local flying, you can’t beat a carbon fiber Sensenich.