I flew my RV4 with a O-320 150 HP fixed pitch prop (pacesetter) and slick mags for about 2 years, then installed high compression pistons (160hp) and flew for 7 more years. Changed to Catto prop, flew for a few more years, then changed to Lightspeed ignition. Flew this combination for about 18 years, discovered a cracked case, which created an opportunity to upgrade. Changed firewall forward to Dynafocal mounts, long gear, O-360 180 HP, E Mags and another Catto prop. I have been flying this combo for 5 plus years. I really thought long and hard about going to a O-320 with lightweight accessories and a constant speed prop - but did not want the complexity, weight and maintenance of the constant speed. So... I went to the O360 and fixed pitch. The weight difference between the original O-320 and the O-360 is about 10 pounds - due to the lightweight accessories I installed on the O360.
My conclusion?? - you can’t go wrong with any of the above combinations. The speed differences and climb differences are a combination of a number of variables, which make it verydifficult to provide comparisons. I am very happy with the current combination. It is simple, reliable and performs well.
I think someone who is contemplating a re-engine project for their RV4 can pick any of the above combinations and be happy with the performance. One can watch the engine market and see what opportunities come along - in other words - keep an open mind to any of these combinations.