Remember head to toe indoors with studio lights (woops forgot to add that )
. The range is 30-50 that I miss. I aslo hate swaping glass all the time. When I had the Sigma it was always used, I sold it and got the 50mm and 85mm. I also do a lot of landscape/ waterfalls and the extra reach would come in handy. I tested a frenids 24-70 and found closeups to be soft i.e flowers may have just been his copy.
The IS will be turned off due to tripoding most of the time.
PS the 35mm "L" did cross my mind

Well, I think you have your answer 
Much as I love my 24-105 as walkaround, general purpose omnirole lens (does Everything And Anything, maybe except photos of wolves at a few hundred yards), when interoperating with studio lighting, I would very much prefer the 24-70. The larger aperture can dramatically influence how you light. Shake is a non-issue since you will have all the light that you need and can generate. There was one event I was covering where I had to bump from 400 to ISO 1600, it had a big influence on ambient light. I would have killed to have two additional stops of aperture (was at f/5.6.. don't ask, I haven't ALWAYS had the nice gear that I do today). That's where I learned that one stop can make a big difference. Then again, the lens I wanted did not exist at that time - 17-55 2.8 IS. It would have allowed me a MUCH better ratio of ambient light to flash, rather than having my subject floodlit with the flash and the background dark. I guess we live and learn.
IS plays well with shutter speed, but since strobes basically 'ignore' shutter speed unless you're in the field and dragging the shutter to allow ambient light in, you don't need it.
Tripod - if willing to carry and deploy - IS is a non-issue either. I take my 17-40 out for low light work, park it on top of the tripod, trip the shutter open for 30 seconds.
Your profile seems to be almost a perfect match for that lens. If you need longer get a 85mm or 70-200.
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