Now I'm having second thoughts about the Sony 10-18 f/4 ... not because I think its bad, but because I recently had a chance to play with the Panasonic GX7 and I am really impressed ... the "silent" shutter is truly silent and I can autofocus by touching the touch screen while I am looking through the view finder. So I have developed real bad GAS for that little camera, plus the prospect of having a 200mm - 600mm equiv focal length in a very small package (100mm-300mm lens) is very enticing and fits perfectly for the kind of confined areas I move in (on our company's rig floor). However, the Tamron 150-600 VC had made my choice very difficult, the bloody thing is just not available for purchase online (our local dealer does have it in stock but he is selling it at around US$ 1800 ... that's a good US$ 580 more than what I'd have to pay through B&H, including shipping and customs) ... so I'm suffering from severe GAS for the past few days
Allow me to add to your GAS problem by noting that you can get excellent results from the Panasonic 100-300mm lens, which through most of its length is very sharp and has great color, contrast etc.; after lugging around bulky, heavy zooms that don't even go to 600mm, I'm always amazed by how small and light it seems (even though it's probably the heaviest M43 lens) - not to mention how good it is. (Based on some user reviews I've read I get the impression there's a degree of variation from copy to copy; if that's true, mine must be one of the better ones.)
Dude, Come on! ... couldn't you reply a few days earlier?
... after reading/watching several reviews of GX7 + 100-300mm lens, I changed my mind and went with the 70D + 100-400 L IS lens on 4 March ... I had the 100-400 L IS before and used it for several years, (it was sold, along with the 7D in 2012 to fund the 5D MK III + 24-70 f/2.8 L II), so I know what to expect from the 100-400 L IS.
But if you had replied 4 or 5 days ago I would have got the GX7 + 100-300, all I needed was one supporting response ... but mission accomplished, you have successfully added more problems to my GAS problem