The five level belongs to the opponents
Most players have a tendency to resolve difficult competitive decisions by "bidding one more". This is often good strategy at low levelS in part, because defense against low level contracts tends to be very difficult. However, at high levels it pays to exercise caution. In particular, it is seldom right to compete over the opponents' five level bid.
Many factors combine to make it usually unwise to bid five over five: a) Even though your hand might be quite distributional, the opponents' hands are often much more balanced. Therefore, you will frequently have more winners against their contract than you might suspect.
b) Partner might have minor honors in the opponents' suits. It is difficult to envisage the defensive power of stray Queens, Jacks and Tens. However, such cards can often help defeat the opponents' five level contract. Other times your five level bid will not fare well because the opponents have minor honors in your suits.
c) In defending high level contracts there are relatively few combinations of cards that need to be considered. Therefore, defenders are much less likely to err against five level contracts than they are to err against lower contracts.
d) Unless the deal is a distributional freak, the combined trick taking potential of the hands (i.e. - the number of tricks you can take in your best trump suit added to the number that the opponents can take in theirs) seldom exceeds 20. Therefore, even if your five over five bid works out well, your profit will tend to be small. For example, suppose the opponents bid 5 6 with both sides vulnerable, and you successfully save in 5 4. If 5 makes, and you go two down doubled, your gain will be only 100 points (-500 versuS600).
e) The combined trick taking potential of the hands is often 19 or less. In these cases five over five bids are often disastrous.
Time and again I have seen players suffer 300 or 500 at five level when they would have gone plus against opponents' five level contract. I challenge you to keep track for several months of every hand on which you compete over the opponents' five level bid. I am quite sure that the points you gain from such competition will be outweighed by the points you lose.
You will find that when the opponents' bid at the five level it will usually be best to defend. Therefore, my BOLS BRIDGE TIP to you is the following:
"Think twice before you bid five over five:
The five level belongs to the opponents."