Actually, epoxy is far less brittle then polyester, and far less fatigue prone that polyester, which is why it is preferable for use with high modulus reinforcing fibers. With all due respect you really made a pretty big mistake by not using epoxy. Epoxy has exceedingly higher secondary bonding strength tp polyester when compared to polyester to polyester secondary bonds. Epoxy is also superior in bridging gaps and sealing out moisture. Epoxy is harder to sand and requires greater care in handling.