A good discussion Oli. And yes, I bet dropping 25 kg steel weight on the floor it not without its hazards!!!

My impression of your result of the 5 min epoxy test, is that the resin only failed over approximately 50% of the tested area. Surely the resin that remains under the bit of hardwood that split off, is still intact, and didn't fail at all. It was the hardwood natural fibre cellulose bonds that failed in this ½ of the glued area, so should not the bond strength be closer to twice what you calculated??.

Adhesives tend to be very specialised nowadays, some are good with wood, some plastic, some metal. Some adhesives chemically bond to the substrate, while others just form a mechanical grip. Some are fast cure just for convenience. Some glues allow for flexibility, some are completely solid. Some are selected simply because they can be easily sanded.

My point is, that while your tests might be interesting as to comparing a group of similar epoxies, I feel it to be unfair to compare say Hysol to Cyno, or clear silicone to PVA. All these adhesives are exceptionally good at their specialized tasks, but will all perform quite differently when asked to attach a servo mount to a piece of hardwood.

In my humble opinion, correct selection and proper application, is far more important than the overall strength of the cured glue.

Roger