Just for completeness, I reported upthread in more than one post how the ATC/STC 17-40x56 left me underwhelmed and after battling on with ownership for a while I sold it on and returned to a CTC 30x75.
Going 'back' was - for me - an excellent decision. Though I'm still unable to offer any direct side-by-side comparisons, the moment I looked through my new CTC I was more than sure that it was optically superior. Plus, the sheer (tripod / formal-rest free) useability of the CTC was a joy to have back in my life.
In a world of hype and skilful marketing, the utterly unfashionable CTC 30x75 is - in my view - something of an unsung masterpiece. Time and again it can be quickly deployed to make accurate distant identifications and with a bright, sharp and very natural image to boot. It just plain works.
In all seriousness, if anyone is considering a ATC/STC 17-40x56, you could do far worse than investigate a CTC 30x75.