You're quite contradicting there yourself. You don't want to fall back in ranks and at the same time you're afraid of having somebody 'too advanced'. Rank isn't everything, and there's a set period of waiting between the ranks while climbing up to begin with, so I bet that kind of approach will only make you more frustrated. Then the skill; if anything, it's rather more important to get along with the master when choosing one. You can learn all the skill, even if 'too advanced', with time and effort anyway. And since you seem to want to keep up with somebody, rank-wise you won't at this point, skill-wise you always can. Take your time and make a decision.
Never discourage anyone who continually makes progress, no matter how slow.
