EOS 6D with Kit, either Canon 24-105 F4 L or Tamron 28-300mm Di VC Macro

[CarlTN]

Thank you for your replies. In this case it really sounds for the Canon, as expected
Regarding my other Canon gear, see post number 5 in this thread.
It should be my "as a good all-purpose carry-around-all-day-so-you-don't-have-to-change-lenses lens" which would be most of the time mounted, at least not while I'm trying to picture wildlife (birds and such) or portraits.
And yeah, for the reasons why I want to switch, read again the initial post. I mean I wouldn't mind getting a crop camera if it would provide the same ISO possibilities and viewfinder size, but that simply doesn't exist from Canon at the moment.
Luckily I'm in no hurry of buying a new camera (first some holiday in the Philippines and Thailand next month), so I might experience the release of the successor of the 7D or 700D before I make my buy decision.
But to summarize my thoughts about the new gear, I want a possible higher ISO for low light images the most

I reiterate my suggestion of renting a D600 with the Nikon 28-300.  Great low light performance means bigger zooms or prime lenses.  I'm a bit confused that you're saying you don't want a crop camera, now you're saying you want to try the 7D successor.  It looks to not be released for another 9 months or so, at the earliest.

[Rienzphotoz]

I recently (Feb 2013) bought the Tamron 28-300 VC as I wanted it for those occasions when I don't want to carry 2 or 3 lenses but on my 5D MKIII it was quite soft and the VC was also making twitching noise (but it worked fine on the 60D) ... so I got rid of it and bought the Nikon 18-300mm VR lens as it is on sale these days ($300 discount ... I think today is the last day for the discount) and also ordered a refurbished D7000.
If your choice is between 24-105 f/4 L IS and 28-300 VC, the choice is actually quite simple, just get the 24-105 f/4 L IS, because you can crop the image to match 300mm fov and still get at least the same or better than the 28-300 VC image quality ... that is speaking from my personal experience of having owned 1 copy of each of those 2 lenses.

[pato]

Thanks all for your valuable input. I will consider it before I buy my new camera I guess it will be the Canon combo