According to Burt Rutan, if you read his book on building composite airplanes and then build a sample, a mix of epoxy and cotton flox or carbo-sil is good enough for use in structural joints for at least generalo aviation airplanes. Are their newer mixes with even better physical properties? Absolutely! But Aeropoxy or West System can be mixed up with structural filler to do a good enough job.

Getting back to the original question, may I suggest mixing up some of your candidate epoxy and cotton flox into a a small cube and seeing how many sandbags you can pile on it. Crude by effective. SO the same with epoxy and another structural filler. You can also mix some up, use it to to join two blocks of say maple together with a carefully measured joint thickness, then pull them apart with your sand bags rigged up to some pulleys. This exercise will give you some rough numbers that you can derate to be conservative.

Generally though, if you have enough overlap on the joints, the glue is not the weak link. And you can make up some test joints and pull them apart to prove that you have enough bonding surface and a good enoiugh bond that the surrounding structure fails first.

So what are you building?

Best of luck,

Wes
N78PS