tedi53 :
better gpu or cpu for 1440p gaming ???
Depends what you have, a GTX 1070 it´s already a good 2k Graphic card, if you can afford go for a 1080. Now it comes as well what you have for processor, it could Bottleneck the GPU a new i5 6600k would mean new Memory new Motherboard, all this augment the costs. you need to give a budget.
Is a 1440p 60hz Monitor or 144hz ?