It strikes me that the justification being used to continue the "tradition" of the IMF head being European - the problems in the eurozone - is actually a very good argument against a European candidate.
A meritorious candidate who can sell the need the change within the affected countries of the EU and then sell the reality of those reforms to the rest of the world is what is needed. I see no good reason why this needs to be a European: there could even be a benefit in it being not being a European in that any suspicions of a "put up" job would be substantially mollified.
European countries represent a substantial minority amongst the shareholders of the IMF - no more, no less. Europe and the USA will sooner or later need to adjust to not having a lock on the top jobs at the IMF and World Bank (respectively). Indeed, the first of the two to accept that might even reap a small dividend from it.