Out of the two I would think the 135mm f2 could give you the most. For me personaly I hardly use a wide-angle lens wide-open. Your Tamron should be just as good for the landscape shots etc. as the 17-55 would be at narrower apertures. The IS is a definite benefit for me, but if you use your tripod more often than I do(very likely) IS plays a smaller role. By the way I guess where talking about days of longer delivery with the 135L right? Not weeks or months I hope?

In the end I'd say buy what you need/want the most.
Quote Originally Posted by ddt0725 View Post
My current lenses consist of the 70-200mm f/4 IS (another one I bought new, sold and rebought used), Sigma 85mm, Canon 100mm macro IS, Canon 200mm 2.8L II, Canon 100-400mm, Tamron 17-50mm (non VC), and I have the Canon 50mm 1.8 II coming today.
To be fair I don't really see the logic in your lens line-up. The differences between the 100-400, 70-200 and 200 are so small that these would have to have a very special individual purpose. I assume the 100-400 would be the primary wildlife lens. The 1-stop faster aperture of the 70-200 would not really make it a low-light wildlife lens. The weather-sealing would then be the bigger factor. The 200mm would make more sense for a low-light lens, however lacking IS makes it less usable as a walkaround lens. Trading the 200mm and 70-200 F4 for the F2.8 70-200 would make sense to me. As well as selling your 200mm to fund the 135L.
Since you mentioned your back-problems I assume you're not taking your entire gear with you everytime you go hiking. What lenses stay at home or in the bag the most? Build your kit from that base I would say. But that's just me