ph0enix wrote:
The OS-X version does not determine the BootCamp version. I've had BC 4 on my mid-2009 Macbook Pro for a while and OS-X has been upgraded a few times since. It's the hardware revision that determines what version of BC is going to work. In my case 4.0 is the highest I can go.
The OS X version determines the version of Bootcamp Assistant, the BC drivers are separate and documented at https://support.apple.com/en-us/HT204048 based on hardware. The major version is the same, but certain drivers will work across different major versions of OS X. Windows can also run older drivers if it is an in-place upgrade of Windows, say W7 to W8.1. If the highest version for a clean install is W7, you can install W7 and then upgrade to W8+ and use WHQL drivers, as long the specific HW drivers are carried forward. W10 is the same way. Most W8.1 versions will work on W10.
ph0enix wrote:
It's working fine with Windows 8.1 but I'm wondering if I should even attempt upgrading to Windows 10. I don't want to break things.
I would not recommend it. Even on more modern hardware, W10 has challenges with GPU, Audio and BT. You should back up and test so you can roll back to a stable Windows version, if you do try W10. W10 will roll back to the prior installed Windows version in case of failures. Driver failures are not always caught very well though.