I've had a few OptiPlex computers and I even think I had a 745 at one point, running Windows 10.
That might have been back in the earlier preview days, I really don't recall.
I believe that the only issue I had (other than the annoying problem of having to remove the CMOS battery just about every time I changed any hardware, and then have to reset the date and time in the BIOS) I think the only problem might have been the integrated Video card driver.
I really don't remember which one it was but I think the MS Standard VGA adapter driver was good enough for what I was doing with it, which was basically test driving Windows 10.
The upside to an upgrade would only be the benefits that come with the overall better resource management which is pretty good compared to Windows 7, however the downside can seriously offset any benefits.
I would strongly suggest making a complete disk image of the system before even considering attempting an upgrade.
https://www.windows10forums.com/threads/please-for-your-own-peace-of-mind.794/
Then I would mount it and inspect the contents to confirm that it contained everything as expected and was likely a viable source to recover from, should the upgrade not go as planned.
We've heard some incredible and chilling horror stories, where upgrades didn't quite go as expected
IF your intention is to go forward, you might want to make sure that you disconnect any extraneous USB peripheral (Bluetooth / Wireless dongles that support mice keyboards, network adapters, etc.) keeping the hardware to a simple minimum of USB Keyboard, USB Mouse and the Monitor..... and remove as in "uninstall" any third party security suites in advance of the upgrade.
Good luck and keep us posted.