PSU, RAM and video card ok....
But if you wish to update the video card, an ATI 7770 is a good mid range cards.
If you do CAD, you may want to look at Intel, but it is expensive.. So if you stay on AMD, get an FX-8320 - fast 8 core CPU, I bought one for video encoding and was so impressed bought another one for sister machine..
Board wise look at the 970 or 990 AMD chipset.. If you had no issues with Gigabyte, they are pretty good. ASRock is very good too as are the more expensive ASUS (I have two ASRock 870 Extremes R2 and an ASUS M5A99 Evo, rock solid).
As for the operating system, ignore all the hype and also the moaning, Windows8 is OK.. As good if not quicker than 7, just takes a bit of getting used to, but really does the job..
If your budget is £600 and you can keep the Case, PSU, RAM, hard drive (s)/DVDRW (proving they are not IDE) you should get a rocking system and have enough for a solid state drive you can run windows off...
I have been programming on computers since the ZX81.
I am an apprentice trained Electronics Engineer with qualifications to back it up.
I have been repairing computers since 1996.
Yet to some people I still know nothing...