It's good advice to strain to declarer on double fit hands, but just how mightily? Suppose your side's combined shapes are 10-9-4-3 in some order, with all the honours in your long suits and none in the short ones. Then, barring ruffs by the defence, your side can make between 10 and 13 tricks depends on how the short suits divide, and so can theirs. If your perfect bidding system tells you your side can make 10 tricks, how high should you save? You can't trust the opponents to tell you, even if their bidding system is equally perfect and they are unwilling to bluff, because they may think they're saving too. You just have to go with your feel, preferring to bid too high than too low. (Ed Manfield's BOLS tip doesn't apply to big double fits — The five level belongs to opponents, except when it doesn't.)
I played in the Camrose at the weekend, and had the opportunity to dice with some good players on three hands of this sort. Here's how we all got on.
This one is made a bit less dramatic by each side's having an ace in a short suit. The par spot is 5X, going one off as a save against 4 or 4, so none of us played there.
If South opens 3, I strongly prefer 3 to 4 for the majors, mainly because I don't want to play in hearts opposite equal length. Over that I like 5 by North, with the proviso that he has to bid 6 if 5 on his left comes round to him. I sympathize with every East-West's decision to bid at the five level, and with every North-South decision to save over it. I don't like the seven-level saves, especially if you haven't bid clubs. And I agree with 6 only if the bidder is right than North-South will save. (Possibly I'm just agreeing with what I did at the table: Certainly I agree with my 5 rather than 5 — 5 is too likely to get a raise.
The best table result for North-South was achieved by Patrick Jourdain and Tony Ratcliff, when North bid 5 then left his partner to guess to lead clubs, as he did not. The best result East-West was achieved by John Salisbury and Mike Tedd, when South doubled 6, I suppose showing good defence relative to what his bidding so far had suggested.