I'm using i7
[email protected] with GTX 660ti.
On 1440p i'm getting around 200-350fps.
Settings are set to low, as game tend to crash (nVidia or Valve bugs)
CS Go loves CPU's more than GPU, so with your budget i would go with 6600k
Z170 motherboard - you can always upgrade CPU.
16Gb of ram - more than enough
nVidia GTX 960 should be ok to play 1080p and even 1440p.
I wouldn't save on PSU - that feeds you hardware, so get a decent one.
Case - can save here
Intel Core i5-6600K 3.9GHz (Skylake) Socket LGA1151 Processor - OEM
MSI Z170A Gaming M5 Intel Z170 (Socket 1151) DDR4 ATX Motherboard
Avexir Core White Series 16GB (2x8GB) DDR4 PC4-19200C16 2400MHz Dual Channel Kit (AVD4UZ124001608G-2
Aerocool V3X Advance Evil Black Edition Midi-Tower - Black/Orange
EVGA 600W 80 Plus Bronze Power Supply (100-B1-0600-KR)
Gigabyte GeForce GTX 960 OC 4096MB GDDR5 PCI-Express Graphics Card
Cooler Master Hyper 212 Evo CPU Cooler
That would be around 700quid.