You're welcome.  Optiplex 7040 Spec Sheet  [IMAGE] I think you meant 7020 and not 7040?  Up to you.  7040 takes 6th gen CPU's. Depending on how much RAM you need, if you have any RAM heavy apps, 7020 has max listed RAM @ 16GB and 9020 @ 32GB.  It's not in specs, but some people have exceeded RAM in 7020 up to 32GB.  If I don't mention it, it'll probably come up anyway. Optiplex 7020 Spec Sheet  Optiplex 9020 Spec Sheet  Tech Guides are available as well.  
I have been happily using my Optiplex 755 MT since it was introduced in 2007, and only problem I have had needed to fix was the front I/O panel (USB port fail), and Processor update. Bios is updated regularly, and I clean the Tower with compressed air twice yearly. Since I can't stand Micro**** Win 10, I will never use it, so I am still going to use my Win 7 Pro as long as possible. I lost my Dell disks in a move some years ago, so would like to find a copy somewhere if anyone knows where. Can I fit a newer Optiplex board in my 775 tower and still use the current installed OS. The drivers will need updating. I was thinking of a 4th Gen. i7 (LGA1150) or newer. I also have a couple of Optiplex 3010 SFF PC's I upgraded to i7 -3770 3.4Ghz 8GB Ram
Optiplex 755 Full Tower