For a unfavorable vul bid, surely that 5C bid can take 9 tricks with clubs as trumps. That leaves little for partner to have in clubs, if anything. Thus I'd bid 5♦ - a X is misleading, as partner is VERY likely to have everything else in the other suits; that is, AK spades, AK hearts and A diamonds. In fact, I'd prefer to bid 6♦ rather than X! NB: The above assumes that the opps bid rationally..... <_<