Being a perfectionist for a Windows upgrade is setting yourself up for a great fall. The only way that I think this can be done with little or no problems is to have the installation disks/downloads for every piece of software you want in your new system, then perform an 'Easy Transfer' from Windows 7. You then install a new, clean Windows 8.1 system, reinstalling the software you require (assuming that everything that you want is windows 8.1 compliant), then performing the 'windows easy transfer' back to your new 8.1 system.
Upgrading always seems to create more problems along the lines of sluggish performance, driver errors, odd freezes, etc.
Unless there is a system on the machine which is a pig to reinstall or cannot be reinstalled which is critical to your business - I wouldn't upgrade but just backup and start afresh using the method above.
I once had to upgrade a shops till system from Xp to Window 7. I had to upgrade as the till software company had gone bankrupt and were no longer trading, and the costs of transferring to another system were so astronomical that the only solution they had was to keep using what they already had. It took a very long time, had a myriad of problems, and ran so badly only the addition of an SSD could make the computer useable.
Upgrading always leaves portions of the old system behind and always makes the system registry huge, and therefore difficult to work with.
I don't understand. If you installed Windows 8.1 over Windows 7 then its already done. There is no (performance) difference contrary to other statements been an upgrade installation and clean installation. – Ramhound – 2014-09-27T23:49:12.597