if you want to do all that then I would recommend a whole new core and take the pariphs (hard drive, optical, floppy, etc...) out of the dell. it'll be a lot more up-to-date, and easier on the headache, when trying to upgrade a dell mobo. (next to impossible sometimes!) also from the looks of it your dell 3k doesn't have an AGP slot anyway...
Figure out what all you do/want out of a system (besides games) and go from there. you would bacisally need: mobo/cpu/PSU/video card. possibly RAM if it isn't compatible with the new specs to what you have now.
Dell 4K S2817Q / Logitech Z-680 / Func MS3 Mouse / Corsair K70
NZXT Source 530 / i7-3770K / Corsair H100 / ASRock Z77 Extreme4 / SoundBlaster Recon3d
Samsung 850 PRO 512GB SSD/Seagate 1TB/2TB/WD 2TB
4x4GB Corsair Vengeance 2133 / PNY GTX 980 ti/ Seasonic M12II 850W