I had no option to go from Windows XP to version 7 after my computer caught fire. The big difference with going up to Windows 7 or 8 (I have 7) was the problem that a lot of the add-on hardware will not work without serious searching for software usually 3rd party to make it work . Most of my early kit was 32bit whilst Windows 7 and the later version are 64bit.
I lost the use of my Nikon LS5 scanner, My printer and the Wacom graphics board. Also I was using Photoshop version 6, with 2 more recent upgrades (CS2 and CS4) and I had to speak to Adobe and ask them to send the download to my computer so I could use it. They have ceased to do this since, so if my computer fails again all is lost as far as Photoshop. Stay with what you have if at all possible it will be easier and cheaper as long as the device is working.
I have tried Windows 8 and just cannot get on with it! As for getting Windows 7, I think you will be hard pushed to find a new computer running Windows 7