YZF & ZZR 600's are surely the best picks of the litter you're looking at - both are comparable in power, handling, comfort, touring possibilities, etc. And definitely dont worry about buying a more powerful bike, gives you growing room and you'll learn to appreciate the additional power/flickability. I can understand being tentative about choosing your next purchase, but you cant go wrong with either of these bikes........personally, I would go straight to a 750 for a guy your size but a 600 will suffice for some years of learning and skill improvement. Congrats in advance on your soon-to-be new-to-you bike!!