Bottleneck - misused term ??
Biggest understatement imaginable IMO.
A GPU absolutely 100% can't bottleneck a CPU , what GPU choice will do will limit fps in games.
You buy according to budget & what you want to achieve performance wise.
The 960 is mid range at best - csgo,lol,sky rim - you'll do ultra 60fps easily - it 100% won't do ultra on new titles with any type of playable fps irregardless of what CPU you own
Newer triple AAA titles like GTA v, division, dark sound 3 if you want 50-60fps it'll be medium to high settings.
High to ultra requires a 970 or r9 390
Straight ultra 60fps requires a 980ti of r9 fury - its as plain & simple as that.
The 960 will play any title out there at playable settings & playable fps - not at 60fps...