You're more forgiving than a lot of people.

Give him an ultimatum....anger management therapy/classes/groups or you are done. If he doesn't get help now, the violence WILL escalate.

No, not an issue with postponing the engagement. I'd say its a good ways away now that this violent part of his temper has surfaced. A lot of men wait until they have a woman "hooked" before showing them their abusive side. I'd postpone any potential engagement for at least another year.