Deciding when your design is mature enough to put in front of a client is always difficult. Unfortunately, there is a natural tendency to err on the side of holding off for longer than we should.
All other things being equal, you should expose your design earlier rather than later - in fact, earlier than you feel comfortable with.
Even if you have problems with aspects of the design, it is better to bring your stakeholders over to your side of the problem sooner.
To use an analogy from card games; play your design out in small "tricks" don't wait for a "full house", lest you be left with a hand full of great - but now useless - cards when the project moves on without you.