Looking for information on these specific Lumix lenses for my future GH5.

I'm going to be buying a GH5 before the summer, and will be purchasing a Lumix lens with it as my base kit (will purchase other lenses in the future, and probably do a lot of renting for certain jobs). I have it narrowed down to three lenses, and can't really figure out what I want to do. This is mostly in terms of technical specs of the lenses, specifically compatibility with the GH5's IBIS, and also a matter of sharpness I'm sure.

The three lenses are the:

• Lumix G X Vario 12-35 f/2.8 ($697 new)
• Lumix G X Vario 12-35 f/2.8 II ($997 new)
• Panasonic Leica DG 12-60 f/2.8-4 ($997)

As for the two 12-35's, I'm assuming that the II is going to be sharper than the I, but will there be a difference in IS? I've done what I think is a lot of research, but can't really find an answer to this. I know the II isn't out yet, so maybe I'm just premature in trying to find this info? What am I paying the extra $300 for?

As for the Leica lens, it's obviously got a longer reach, but the trade off being a non-constant aperture. What kind of quality differences are we looking at here as far as Lumix vs. Leica glass?

This lens is meant to be a walk-around photography lens for hobby reasons, as well as for basic corporate video production purposes. If I really need reach, I've got an old 50mm Canon FD lens, and a 70-210 Canon FD lens, so I'll be getting an adapter for those. I'll be getting rid of a Sony X70 to buy this, so any of these Lumix lenses will be pretty comparable to my X70 as far as capabilities for my more basic freelance jobs. But I do want something that will match or exceed the sharpness of the X70 Zeiss lens, as well as take full advantage of the IBIS of the GH5, which is why I really want to go with a Lumix as my first lens.