So I have not been able to find any information on this subject, I have an optiplex 980 DT, it has already been upgraded so to speak. Currently I am running

windows 10

16 GB ram

intel core i5 650

Radeon HD 7750

The motherboard is the stock board and the power supply is a 255w 

I am wondering if 1. I can upgrade my graphics to a newer better one and 2. if I can do the same with my processor.

I bought an intel i5 680 but it didn't take, it outright told me that, that processor was not compatible, Currently I am thinking of buying an i7 870, and either upgrading to the Radeon HD 7790 or going with the NVIDIA geforce gtx 750, first I would like to get some opinions we are looking at an upwards of a $500 buy and I would like to know if these would even work. Any help is greatly appreciated!