DDR4 1.5v

Ya it must have been that Bios. I seem stable at 4.6 GHz as well with 1.344v under load, 1.328v at idle. Possibly with some more room for voltage adjustments.

Are the kaby lake Bios and Processor working well on the Z170?

Depends on the board. But mostly yes frkm what (little) I have seen.

I was having issues with version 3007 with Skylake Cpu. I hopped over to the ROG Forums to see if it was just me and it seems hit and miss. But it's very early. I imagine another month or two the Compatibility will be far better. I am inclined to keep my board if that is so, it has done good for me and it has a Great Power Phase Design. And TBH I would rather wait and dump money into an overkill x299 rather than dump more here but......in the end it is just money.

I doubt that all motherboards will have all issues fixed as manufacturers have released one quick update and now try to focus on Z270 boards. What more most KL BIOS releases for Z170 were about a month before KL premiere.
ASUS ROG has better support and I guess that ASRock as always will try to fix all the can but I have my doubts in Gigabyte or some less popular and cheaper MSI or ASUS boards.

Most updates for Z170 motherboards which I was checking look like 5-10 releases, 3-6 months nothing, KL update, 1 month+ nothing. Even boards like ASRock OC Formula have only 1 update with KL support since about March last year.

Micron lists 1.5V as the absolute maximum for some of their DDR4:

I wish I would have found this thread earlier (helps to look in the right place eh?) Switching my RAM to 1.490 (seeing 1.500 volts when in windows) was the only way for me to be able to get it to run stable, at a decent clock over anything but the XMP profile. Seems to be doing OK so far and doesnt get warm at all.