Hi,
Just picked up the 5D3 this week and got some time to fiddle with it last night.
Upgrading from a 30D I am overwhelmed by the results as I went for the high ISOs 6.4k-102.4k!
a) My first impression:
The 5d3 vs the 30D delievers about 4 stops better high ISOs in RAW, which to me is a huge step!
51.2k without NR still seems to look better than ISO 3200 on a 30D, both exposed to the right.
ISO 12800 is a no brainer now! Even without NR, if well exposed.
Even a 102.4k image is kind of "doable", although with some heavy NR, but I am geared toward Robert Capa and Robert Frank Style photography, so there is no problem with some noise for me. I do everything in DPP and convert b/ws using an old CS2.
The 5D3 is absolutely worth its money from my point of view and a tremendous camera!
Therefore:
b) What will be the standard high ISO level after the 2 next bodycycles of the 1 and 5 series?
Is it likely, that my extended ISO 102.4k will be the ISO 12.800 or 25600 6-8 years from now, then we would talk about extended ISOs on a 5Dwhatever up to H1 204.8 (like 1Dx now) and H2 409.6k
A 1Dwhatever would even break the million mark by then going up as high as ISO 1.638.400!
Whoever will benefit from such a high ISO...

Does all that seem likely according to porbable upcoming sensor tech improvements or is that too much of wishful thinking?
I am not too much into tech. So, what do you think? Any corrections and contrary/more realistic input is highly appreciated.
Anyway, the 5D3 rocks! 8)
Cheers, Pedro