I have owned the 12-35, the 12-60 3.5-5.6, and the Oly 12-100 f4. Recently I had a chance to use the 12-60 Pan-Leica for a day.
Not knowing your use I can't say how important the extra stop would be to you, but it has not been an issue for me.
I owned the 12-35 and 35-100 for a year or so and the 35mm limit drove me bonkers. Seemed like I was changing lenses more than I was shooting.
So I swapped to the 12-100. It is a killer lens. Very sharp. Great IS, even though it cannot use the Pana dual mode. Great range, at least for what I do. On the downside, it is heavy and bulky, though considerably smaller than a 2-lens kit. The other downside is that for a portrait photographer it is a bit harsh, especially if a subject has any skin problems. I'm very often adding a touch of blur in my processing (in addition to I usually keep the camera sharpness set one step down from normal).
So I picked up a used 12-60 3.5-5.6 as a lighter alternative. I had owned this lens before and knew I would be happy with the performance. In addition to being smaller and lighter it is also a bit kinder to my portrait subjects.
Finally, the 12-60 2.8-4. Not long ago I was able to swap for a day with a friend -- his 12-60 for my 12-100. I think I could really love this lens. Very high resolution without the harshness of the 12-100 -- typical, I think, of Leica lenses. Perhaps a bit of fall-off toward the corners, but not much.
Bottom line, in my opinion: Unless you really need f2.8 skip the 12-35. I would pick the Oly 12-100 for hard-edge subjects such as architecture, mechanical subjects and maybe landscapes. I'd take the 12-60 Pan-Leica for portraits. The slower 12-60 is a more that adequate substitute for either if 5.6 at the long end is fast enough for what you do.
(As for the variable zoom in video, so long as you set the aperture to the long setting -- 4 or 5.6 in these lenses -- it will not vary as you zoom.)
Gato