10 is the better option, you'd spend a ton of time catching up with 8.1 - loading updates and catching up on drivers.
the GTX 750 Ti is on nvidia legacy drivers. so it should be easy to locate.
Have done similar upgrades on FX970 platforms (FX6300 and 8310) and they've been painless.
You can do a Windows 7 image backup (and make a repair disk) if you have concerns - that should be able to restore your system completely. Acronis is also a good backup solution. Both should be able to get your original system back if needed.
If you've done the upgrade before it should go fairly clean. For boot issues after migrating to Win 10, you also can do a Reset, so it re-installs clean but keeps your data files.
I'm another one of those strange people who has encountered few problems with Windows 10 (since RTM) on older hardware (Core2 Extreme desktop, 1st Gen i5 laptops, even a cheap Atom 2-in-1). For the upgrade from Win7, though, a clean install from media is certainly the way to go. You're going to reinstall all of your software (consider this an opportunity to update all of THAT too!). So don't worry, just back up all of your data (don't forget email databases if you keep them locally) and perpetrate. Following is kind of a rant, so fair warning!
In my case, upgrading (and doing the semi-annual feature update which is usually a full service pack or o/s replacement) was made easier by the fact that I have long kept my data on a separate D drive, so only working stuff is on C. Yes, pictures, music, etc. need to be saved to the backup - those are usually some of the working files on C. It's perhaps tedious (I just spent the better part of a week updating my entire chain of internal and external data and image backups for several computers around the house at the end of the year, all using the built-in tools in Windows 10 - Acronis is nice but you can do without in a pinch), but necessary. One thing that Win10 has, that wasn't available in 7, is File History backups (you need a separate, preferably external drive to do it) that automatically versions your files, which might make future backups a little saner.
I have a GTX750ti in my Core2 Extreme desktop with Win10 Pro. It still uses mainline GeForce drivers from the nVidia website, not legacy drivers. How long that will last is anybody's guess, but I don't think it's been quite pushed off to the graveyard yet. I do avoid the GeForce Experience app - I just manually download and install the driver package with Experience unchecked every few months. Still fully supported as far as I can tell by both nVidia and Windows 10.
Be prepared to pay for your copy of Win10 - free upgrades in general are long gone unless you can fit some fairly restricted classes of users. That said, the upgrade price isn't much more than it was when I went from XP to 7. If you can afford it, I'd recommend going with Pro rather than Home - similar base o/s, but Pro has a lot more flexibility wrt system customization and controls.
And yes, I've done a "Fresh Install" or "System Reset" several times on some of my computers when they started to get slow or kick out a lot of errors. The tiny tablet is the worst for that (Win10 in 2GB RAM, Atom 1.3 ghz CPU, and 32GB max of C drive - what could possibly go wrong?). The good thing is that, yes, you can (usually) do it without wrecking your data files, though having a backup is still a good idea - the time you don't is when it
will mess things up (I'm a firm believer in Murphy's Law). The bad thing is that it
is a reinstall of the o/s, so you will have to reinstall all your software again and start from scratch on its settings.
Finally, one major difference between 7 and 10 is privacy (not security - 10 is better for that - but privacy). Left to itself, a new Win10 install will make your computer about as private as your Android phone: it insists on installing with a MS account as administrator, collects all sorts of data about you and what you're doing, and so on. Much of that is controllable, but you have to be vigilant both during the install process and when trawling through the system settings afterward (which you definitely should do). And contrary to popular belief, it
is possible to have your critical accounts local, still, and it
is possible to link to your MS Account from a limited-user account on the computer and keep it limited user. There are some 3rd party tools that can help (e.g. Spybot Anti-Beacon, ShutUp10, and several others), mainly by providing a consolidated front end on the Group Policy and registry settings that control many of those behaviors. You can do most of it from the various Windows settings, too, but the 3rd-party ones might be easier to understand.
Edit-PS: fwiw, I even had a Windows Phone that I managed to hack W10 into and it worked quite well overall. Lumia 635 (512K RAM) that MS would not officially support W10 on. Got it onto W10 during a brief period when Insider made the upgrade from 8.1 possible, then (after dropping Insider and being auto-upgraded to 1607 - which was the best mobile o/s MS ever did based on how well it worked in that phone) a little registry hacking moved it on to 1709 (the final version of W10 Mobile). It eventually died of a hardware failure, so I now have an Android, but Windows Phone was really a quite nice system if you only needed fairly ordinary apps. Just another indication of how Windows works surprisingly well on old, if not truly obsolete, hardware.