They say the 17-40 and the 50 f1,8 is a bargain amongst lenses, well, it's nothing compared to a used 135 L. It's THE best value for money.
Sick sharp and blasting AF, precise also. Very nice balance on the camera, and as you say, it's not so IN YOUR FACE as the 70-200's.
Get one, you'll never trade it off if it's the focal you want. Personally I hardly ever use below 24 and over 50 with tsometimes the 85, so not for me. But IQ wise, it's killer....