Just out of curiousity, has there ever been an incident (let alone accident) where a crew dawdling in raising the gear (but doing so eventually) has caused the problem? I can't offhand think of one.
The reality is that even single engine performance has margins built in, and considers a case usually much worse than the case of the day. I'd be really shocked if an extra, say, 5 seconds in initiating gear retraction in any remotely routine OEI condition represented a meaningful safety reduction.