Yes Gus, the slower epoxy form longer molecular chains and are stronger than the slower. I shy away from the fast epoxies (5 minute) for a number of reasons unless the repair is not structurally important and brittle joints aren't a problem. 5 minute has its place, it is just very limited. In case you do not know it, the fast epoxies take nearly as long as the slow ones to gain full strength, usually a matter of hours--not minutes. It is just that the tack period is shorter.