The strength of epoxy is determined by the length of the molecular chains that form as it cures. Epoxy does not get its major bonding power by physically grabbing a hold on the two pieces being fastened together but by the molecular bond of the atoms in the pieces being bonded and the epoxy atoms, very little to do with how well it soaks into the parts although that has a slight bearing on the strength of the bond. Yes, the slower cures are stronger than the faster ones as the molecular chains formed as it cures are much longer. Perhaps there is a chemical engineer reading this that can provide a more exact and accurate description of how epoxies work.