A compact telezoom better than the EF-S 55-250 f/4-5.6 IS II ??

I have the Canon EF 70-300 f/4-5.6 IS USM, but are tired of the weight and size of this. I always end up leaving this lens at home when traveling or going for a photo walk, because of its size and weight (630g).

Ideally I would like a compact "prosumer quality" lens with IS, USM and Full-time Manuel Focus (=> Canon ring-USM or similar). I found the Sigma 50-200mm F4-5.6 DC OS HSM which have both image stabilization and "Hyper-Sonic Motor", and are compact and weights 430g. And a further advantage are internal-focusing with a non-rotating front element. Though I don't know if Sigma's HSM technology allows full-time manual focus, it does - on paper - looks like the closest I can get to my "dream lens". However reviews I have found of this lens seems to imply a half-bad optical performance, especially in the long end (which is the most important end for me).

It looks like the Canon EF-S 55-250 f/4-5.6 IS II optically are a much better choice, so at 390g this is currently the best choice I've been able to find. But I would happily pay the double if I could find something with better build quality, better optical performance, USM (or similar) and Full-time Manual Focus - combined with modest size and weight.

Are there any other options out there that I have missed?

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Stig (Copenhagen, Denmark)

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