I'm sure this has been discussed before, but it's a new topic to me. MY longest focal length lens is the 80-400mm VR, which as far as I am concerned produces excellent IQ when used properly. Unfortunately, the AF leaves something to be desired as far as speed is concerned. The 70-200mm VR certainly has excellent IQ and on top of that it has lightning-fast AF. Unfortunately it has only half the reach. I've been considering the TC-17E II teleconverter, which would give me almost the reach of the 80-400mm VR, when added to the 70-200mm VR. I've read all the warnings about using teleconverters with zoom lenses, which is why I've eliminated the TC-20E II from consideration. I don't need that kind of reach often enough to indulge in the telephoto primes. So, I'm wondering if those of you with first-hand experience using the 70-200mm VR can tell me if I'm stretching, or if getting the teleconverter would be worthwhile. I guess my question is how much IQ and AF performance do you lose with this lens/teleconverter combination, assuming proper technique?