pnodrog;778263Another story if you do need a fast lens due to lighting or for aesthetic reasons but very seldom is their superior image quality of any particular benefit. Fast expensive lenses certainly do not make an unskilled photographers images any better.
+1 to what Paul says, and I'm about to put the "Another story" to the test.

Each year I photograph between 2 and 4 concerts performed by a local choir in a church (not always the same church but always with lighting that is, shall we say, somewhat testing). I kept the relatively heavy f2.8 105S Z series prime mainly to use as a macro/portrait lens but also for possible use in these conditions if the slower 24-200 gets pushed too much. And of course even though the IBIS in the Z bodies is superb the singers and conductor are not exactly motionless . We'll see how things go in a couple of weeks.