RE: 65% or 80% let off, which do you choose?
If the biggest concern is accuracy, it would seem to me that more important than any particular percentage of letoff reduction, would be a defined draw weight to hold. If one person is drawing 75 lbs with 80% letoff, the holding weight is 15 lbs. If another is drawing 50 lbs with a 65% letoff, then they are holding an almost identical weight - 17.5 lbs. Assuming draw length is the same, both situations should have the same torque at full draw.
Rather than advocate a percentage letoff, I think a particular holding weight would be a more appropriate goal. If a target shooter can be reasonably accurate shooting 50lbs at 65% letoff, then a bowhunter shooting 70+ at 80% letoff, shouldn't be at a significant disadvantage. Does anyone know at what holding weight the negative variables are reduced?
Also, when holding on an animal at full draw for a minute or more, 10 additional pounds of holding weight can indeed be significant. Accuracy can really suffer when you start shaking from a long hold at full draw, while waiting for just the right shot. The few extra fps speed from the 65% cam would be a poor trade off when comparing to the added hold-time of the greater letoff, in my opinion.