Miserere Mei , Oct 05, 2010; 06:18 p.m.
Vincent, it doesn't really matter if the Sigma is a good choice or not, because it's the only choice for K-mount. Unless you want to spend a lot more on the outstanding Pentax 31mm f/1.8 Ltd. But for concert shooting (which I've done a bit of with the K10D), every photon counts and the f/1.4 of the Sigma will be very useful.
What lenses are you using now?