The only reason that the Mac Pro 5,1 is supported in Mojave (if support for the machine actually ships) is because Apple feels bad about screwing over their Mac Pro customers repeatedly over and over and over again. If there is a future for the Mac Pro it is coming next year and you should buy one and hold on to it tight. If Apple's comes out with yet another sealed up box then it will be a serious time to consider Windows 10. It will no doubt be pricey brace yourself for that but as long as it is expandable