You will get different answers from different people. The chip throttles over 100C to protect itself so Intel must have thought that anything below that wouldn't kill enough CPU's within the warranty period to cost them too much money.
Beyond that, "cooler is better".
Personally, I would only be ok with 74C if it occurred under absolute max load in a synthetic stress test like Intel burn test. Even then, I would probably be on the lookout for a sale on a higher-end cooling solution.
looks like it's time to crack open the side panel and point a fan inside until new heatsink gets here -.-