A 'documentary lens' for the GH2

THE LUMIX 14-140: THE MISSING LINK..UHH, LENS?

I'll be starting filming for a new documentary pretty soon and I am researching what lens would best complement some lenses I intend to use. My Panasonic Lumix 20 mm 1.7 is the one for wide shots, establishing, the Canon FD 50mm 1.4 for interviews and then I want a zoomlens for run 'n gun. I'm thinking the Panasonic 14-140 because it has received positive reviews (especially for video purposes), it's a versatile lens and with the new firmware (touch-)focus is supposedly even faster. It's not a fast lens at 4.0 but with the Pannie 20mm at 1.7 and the Canon at 1.4 I should have that base covered.
I'm primarily looking for a lens that will get me out of a tight situation, whereby I can reframe without moving and that will focus fast and accurately without external monitors. Another reason to buy Pannie lenses is because I think the 20mm 1.7 is a lovely lens. I love the 'velvety' yet sharp look.
The Panasonic 14-140 not what you'd call an affordable lens at €680,- but I should be able to get a better deal on a used copy on eBay. Or I can buy a body plus 14-140 lens because they are cheaper as a set and then sell the body...

If anyone has suggestions for a good zoomlens that meets above requirements, let me know!