GPU for poe

Hi guys, can somebody give me an advice :
im using very old pc - i3 550 3.2gz CPU and GPU geforce 450 gts 1gb. And ssd. And now i can take from a friend geforce 970 4 gb and curious - will this be much better for poe or old cpu will bottlneck hard and there will be no profit from GPU change? and which options in game affects only GPU (so if i will install new one - what i can raise for better looking game without making CPU working harder) like what..textures i guess affects only GPU? and what about skills - for example lags from molten strike vs any other low skill means that its GPU heavy or CPU?
thx for any help...