A quick note, which some may find useful?
I've just got back from a 6 week tour of a lot of different types of places around Australia with my SL - visting family in Perth for two weeks and then travelling around from Adelaide to Cairns.
From my modest selection of lenses, I took my M28 Lux, M75 Cron APO, and the SL 24-90.
I thought the 28 would be useful for cities, the 75 for family portraits and the 24-90 for anything else.
I can report that the 24-90 was on my SL for 95% of the time, and delivered some really great photos.
The only other Lens I used was the 28, when doing early/late walkabouts around Melbourne at the beginning of my tour - great photos, good in low light, and more discrete in some "lively" places in the bustly evening city centre.
All other times, although heavy (compared to the Leica M lenses), carrying the SL+24-90 wasnt a real problem in spite of many hours of walking.
I did appreciate its weather sealing, when photographing windsurfers with lots of sea spray around, and not having to change lenses in dusty conditions.
So, my reccomedation would be to not to be affraid of the 24-90's weigh penalty as its benefits outweigh the dissadvantage - and with outstanding photo quality.