Thanks for the quick replies!
Just to clarify, wildlife isn't a major consideration but sometimes it's great to have the ability to go long at a moment's notice if I spot some photogenic beast (distant seals, shy reindeers, that kind of thing). But still, it's all about compromise.
The DA* is beyond any budget I can reasonably justify, unfortunately - but the Sigma 50-150 is something I hadn't seriously looked at, good idea. Cost is not much more than DFA 100 WR either, though it is twice the weight and bulkier. Hmm!
That K135 F2.5 is new to me, looks like a really good idea except that it might well be disregarded in the way my other MF lenses were. Having said that, I lose nothing by buying one and selling it again if it gathers dust. Could be a plan, thanks - sometimes it's helpful to ignore parts of the question.
As far as the 55-300 goes, it may be three times the price but my Tamron is very good for the price (I think) so I'm aware it's not a straight case of comparing costs. The resolution is definitely what I'd like to improve, so if I'm still going to be less than overjoyed I'll give this one a miss.
Very helpful, not quite decided yet, more opinions very welcome...