Just a plain comment by a plain man, Windows is Windows, and if you once used 3.11 or Windows 98, using Windows 7 isn't very different, nor will Windows 8 be, probably. Windows 7 can be accustomed to Windows 95/98 look and function, highly. I'm quite convinced that a future Windows 11... whatever, can too.
I'm with Windows 7 Professional, no keen interest for Windows 8. You can always buy a computer AND OS plus other software separately. About reusing your Dell key - major manufacturers quite often limit their OS versions to their own computers, quite the reason for me to buy INDEPENDENT computers combined with FULL VERSION OS. No one tells me about my PC, it's mine totally, and my Windows 7 Professional is guaranteed support to 2020 or 2024.
The grand word... Freedom.