The 800 gave me more wide open power but the 650 had better driveabilty and throttle response.
So it sounds like the Rev-O-Nator is adding advance as rpms rise to kind of mimic the VA or to compensate for latency . I think it would help if you plotted your timing in 200 rpm increments up to 3800 or whenever it stops advancing . Then we can figure out which VA can you have and start tweeking that.
The reason timing is important to A/F is that if your spark is late there will be unburned fuel (or still burning) passing the O2 sensor making you think the jetting is rich .