If the PC you’re building has the latest and greatest hardware in it, you might find that Linux might not support that stuff yet. You might get lucky, but you might not either. It usually takes a little while to get new hardware supported. So it might be a better idea to install Linux on your older computer, then there’s no reason to buy a new PC anyway. Linux uses about half the RAM that Windows uses, for example, so it’s like you did an upgrade anyway. As long as you have over 4 GB of RAM, you’re fine for desktop usage. Windows requires 8 to run as well that Linux does at 4. You’d only need to upgrade if you’re after extreme gaming support.