I only want two things in the 7D2. Less noise at higher ISO -- ideally a 2 stop boost.
I seriously doubt that's possible.
The one feature that intrigues me about the 5D3 is it's performance in low light. Based on researching online reviews, I estimate the benefit to be about 3 stops over the 7D (and my 60D).
Not even close. Slightly more than 1. Much less than 2. 1 1/3 is what you'd get from nothing but the larger sensor so this is about right.
You might be looking at JPEGs. The processing engines in the new cameras are quite good, but the raw data hasn't really improved much since the 7D came out.
Have a look: http://www.dpreview.com/reviews/canon-eos-5d-mark-iii/28
Select the 5DIII and the 7D. Compare 25,600 on the 5D to 12,800 and 6,400 on the 7D.