I plan to do a pc upgrade very soon. Alongside that I plan to start with Mint or Fedora. Is there any real or big downsides to dual booting ? Aside from the harddrive space lost ?
If I like or really like my time with Mint I would probably switch permanently but I felt like I wanted to test it for a couple of months before making a complete switch.
Im a big 
so that impacts my consideration. Dont really play much multiplayer shooters so I dont have a problem with kernel anticheat games not working.
If the purpose is to get a feel for the OS and check your compatibility with it, I'd recommend just running a VM with your distribution of choice on the Windows install
It should prove way less of a headache and youll get your feel of it anyway
I agree with this, but they won't be able to easily play games that way because VM 3D graphics are weird.