Best Upgrade for my 960

Either of those will be a substantial upgrade over what you have -- but since you're running Photoshop, make sure the system you buy has a discrete video card -- taking a slightly slower CPU over one in a system without a separate GPU is a better idea than the faster CPU in a system using only integrated video.

The 990 is an older series of systems than the 7040 is.

Do you want to better understand what it is you're looking at or do you just want a yes/no answer? Because, it would be better for you to understand what these things are and why they are priced the way they are before someone gives you an answer.

I would be highly skeptical of anyone who would sell an i7-6700 equipped computer on eBay in November of 2017 at anything even remotely that price. That machine is barely a year old, and the processor alone is worth more than the entire price of the machine: https://www.amazon.com/Intel-I7-6700-FC-LGA14C-Processor-BX80662I76700/dp/B0136JONG8. 

I hope the link worked - Dell's forum tools are atrocious - but I tried to link to the processor on Amazon.com for $270.00.

Ok..so can I turn off the gpu in the CPU and install a video card? I have a pretty good card in the 960 so can I move it over to the newer one?

Thanks for the quick response

I would love to better understand not just buy because there are so many model numbers it is impossible to know what to do.

Any help in understanding will be greatly appreciated.

Let's hope I can withstand Dell's awful forum (and it's incredibly STUPID Capcha implementation ... as though it's really necessary to ensure that answers here aren't from "robots"). Given all of that, here's the point of my original post ... those are completely different machines.

The first one is a sixth generation i7-6700 machine, which is a very recent processor (and very powerful). Intel is currently on the 8th generation for desktops. The second machine is a relatively old  i7-2600 (second generation) processor. It is less capable than the first machine you listed (in fact, I wouldn't buy anything less than an i7-3XXX series processor at this point).

So, while both of those machines would be better than what you currently have, the first one would clearly be better than the second. Here's the problem: when someone is trying to sell you the first machine for less than $200, I would be very skeptical of the supplier. Is he/she selling "hot" goods? Why is it so cheap? 

This is a great page for comparing the relative merits of PC CPUs: http://www.tomshardware.com/reviews/cpu-hierarchy,4312.html. 

I hope this has been helpful.