135mm + 1.4 extender _VS_ 70-200mm f/2.8 IS mkI

[rs]

the 135L isn't the sharpest partner for a 1.4x TC:

http://the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=108&Camera=453&Sample=0&FLI=3&API=1&LensComp=687&CameraComp=453&SampleComp=0&FLIComp=3&APIComp=0

The 1.4x TC is a much cheaper (and lighter) option than the 70-200 II, but if you can afford it and don't mind the weight, the 70-200 II really is something else.