AMD chips have always been cheaper than Intel, and if the AMD Zen chips are what they say, you could save over $100. by being patient and use the Zen chip. Either way you go, you'll need a new motherboard/memory
My Optiplex 755 MT has the 'good' motherboard with a 75W TDP max as printed above the slot, not the 25W version. It's also the motherboard that can take the quads. Without those 2 things I wouldn't even think of wasting my time with it. The other mobo was the one that was shared with the desktop version of the computer. I've Always built AMD, all the way back to an AMD K6 box which I recall ended up overclocked to 400mhz. I've always built AMD because I always built to a price/ value. But I wonder if I would get a better value if I got a decent Intel, just not latest and greatest. If that would be a better deal and still project 5 years or so and still be fast enough.
I can't do it. I can't justify spending more for less because I like the idea and to prove it can be done.. I started looking into Optiplex 980 motherboards, and modifying the rear I/O of the 755 case so I could have a 1st gen I7 powered 755. But dollar for dollar aside from the cool factor it may have, there is no point. a 980 on it's own is dirt cheap with a base I5 650 processor, or I could spend just a little bit more on a Precision T3500 w/ a decent quad or hex core Xeon and 12gb ram. My Radeon 7790 would be 'ok' for a start and I could live with it for a while. Or a motherboard, processor and decent case to 'rebuild' my old computer would probably be around the cost of the T3500 if I really looked hard for deals. I have a retail version of Win 7 pro so it's not a big deal to have an OEM COA/ SLIC although, my Optiplex 755 does run a modded bios
I ended up Settling for a T3500 With X5670 and 12gb of Ram and a 1TB HD for $228 shipped. I'll stick either a 1050 TI in the slot or my Radeon 7790 to hold me over for something nicer.. I couldn't waste the money on the Optiplex 755 and this just seemed like a lot of bang for the buck. I know it is older tech still but I think it will hold it's own for a while.