Sorry to maybe sound a bit stupid here but if I am already running win7 under Bootcamp and If I upgrade to win10 when does the Bootcamp upgrade happen ?
I installed Windows 10, then installed what I had available at the time (just days ago) which was Boot Camp 5 being then the most recent even though not specifically for Windows 10 and all was well once I did that. I will say, prior to doing that install (of bootcamp drivers) on my own particular system, Windows 10 performance was horrible and even the Boot Camp installer took forever (like an hour) to run and finish but it did without errors and after a reboot, presto! Good to go. This was upgrading from Windows 7 in my case. I forget if I already mentioned that above or not.
So, I mention that just in case you do it and then it seems like it is screwed up. Installing the drivers once Windows 10 is installed corrected everything here.
Today, after learning about the release of Boot Camp 6, I ran the Apple Software Update utility from the Windows 10 start menu to upgrade to the most current Boot Camp drivers, etc. I don't know if that would have worked or not to install the Boot Camp 5 ones after installing Windows 10. I presume where I upgraded on top of Windows 7 that I would have had the updater available to try but it did not occur to me at the time. So instead, I just went to the Apple support pages, found the bootcamp area and downloaded the drivers installer from there for my particular iMac.
I hope the way I just worded all that isn't confusing. Basically it went like this:
Install Windows 10 upgrade on top of Windows 7
Download and install then most current Boot Camp from Apple Support web site (while in Windows)
Today, used Apple Software Update to update to newly released Boot Camp 6
So, doing it now I would try this:
Upgrade to Windows 10
Try to run Apple Software Update from the start menu in Windows 10 to install latest Boot Camp
If that doesn't work, download the installer from Apple Support website and do it that way.
Oh, and that didn't sound stupid at all. You want to see stupid? You should see how often I dive in and screw up and only then learn how I was supposed to do stuff. lol