According to the statistic table if you have 9 trumps it is very good news. 40.85% of the time your opponent has 8 trumps, 41.63% of the time your opponent has 9 trumps, 14.60% of the time your opponent has 10 trumps, 2.71% of the time your opponent has 11 trumps, 0.21% of the time your opponent has 12 trumps. About 40% of the time your opponent has the same number of trump as you have which is 9 or less then you have with 8. With 9 trumps you always bid up to the 3 level. Never bid to the 4 level. If your opponent bid to the 4 level, you should double unless you have other reason that indicate you should not. Statistically more then 80% of the time your opponent will go down according to the Law and the statistical data of a general hand.
Even better results are shown by double dummy analysis. Bid more or double more often with 9 trumps.