i have the same spec as you
don't change the CPU, just overclock it at 4Ghz.
and take a GTX1070
i have a GTX980, and i can play at 1080P at full with all games.
and sometime in 4K !
my spec :
-Carte Mère: Asus Maximus IV GENE-Z
-CPU: Intel i5 2500k @4700 h24 (46*102,2) (@5100 en bench) GROS VCore :/ mais tiens bien depuis 6 ans !
-Ram: G.Skill RipJawsX 8Go(2*4)DDR3 PC3-12800 + 8Go autre !
-Ventirad: Corsair H60 push/pull 2*NoiseBlocker SilentPro PL1 900rpm
-SSD: OCZ Agility2 240Go
-HDD: WD Green 2*2To + Seagate ST2000 2To + Seagate 5To (un Seagate HS :/)
-Alim: Corsair Hx750w
-Carte Graphique: Gigabyte GTX 980 "N980G1 Gaming 4GD" "4K POWAAA !!!"
(AVANT -> SLI eVGA GTX570 SC)
-Boitier: LianLi v354b
-Ventillo: 2*NoiseBlocker SilentPro PL1 900rpm (120mm) sur le H60, 120mm LL sur façade, 120mm LL extraction arrière, 140mm LL sur TOP
-Ecran: Samsung 24' B2430H (1080p, HDMI/DVI/VGA)
-Son: Logitech Z323 - Enceintes 2.1 RMS 30 Watt - Noir
-Casque-Micro: Astro A50 (Compatible PC/PS3-4/Xbox 360-One)
-Clavier: Logitech Dinovo Edge (HTPC --> génial)
-Clavier Gaming: Razer Nostromo
-Manettes: GamePad x360 sans fil, + GamePad XboxOne
-Joystick: Saitek x52
-Souris: Logitech G700
-En double écran: TV UHD/4K LG 55UB850V (WebOS, Dalle IPS)
-Casque VR: Oculus Rift DK2

(revendu)