Originally posted by tibbitts I find the 10-20mm very useful, but if you don't need the wider end, it probably would not be my first choice for use at the longer end. At 20mm it's slow, and you'd then have a big gap to your 28mm. You could get a 16-45, if you can find one without the front barrel wobble, or a 17-50mm Tamron, or 17-70mm Sigma, etc.
Agreed re: the reason you'd choose the 10-20mm... or not.
Just to express a point of view, I would consider the 26.5mm to 43-46mm FF-equivalent focal range "where it's happening" for a majority of skilled photographers who use small format cameras to best advantage. I couldn't kick about a 52mm equivalent, though it's not so much to my taste on APS-C. Though to each his own... I want the best I can get in financially sensible (personal, not categorical) terms in this range. Unfortunately, no one as yet offers a photographically sensible, balanced mix of primes to achieve that goal gaplessly in the APS-C format -- the way we had it for film in the '80's -- not from my perspective, anyway (which biases in the direction of landscape/cityscape, "cultural documentary"/travel, etc.) Nor a zoom, either, of both modest proportions & weight, AND class-leading, prime-challenging performance. I have no particular argument with pixie dust effects justifying lenses... but you can't really cover the broad territory with pixie dust. That's an IQ first kind of perspective and may not jibe with others' valid priorities. But I'd argue that those other priorities are better being met by the existing options, in comparison. And one would need, too, approximately the traditional 85-105mm FF-equivalent telephoto to round out the kit to cover the most useful FL range. Specialists need what they need, of course. ...Though people buy what they THINK they need... which isn't necessarily the same thing -- a particularly hazardous pitfall in the internet age. End of editorial.
P.S.: I surely do wonder how the projected 12-28mm wide zoom will turn out. I'd like to think it will be one market-friendly, what you can reasonably expect in the real world kind of lens on the quality front... not too big and heavy (Pentax style), but not biased toward "cute" either... fast enough... low distortion... and competitively priced for the performance on offer vs. Canikon. And no AF or reliability issues, please! Am I dreaming?