Overwatch is a really well-optimised esports game. Simple answer = Yes (up to 1440p)
4K is still quite demanding, you'll really need to break the £1k barrier (and some) for 4K at the desirable 60 frames per second mark.
Now at 1440p this rig coupled with Freesync would still pump some lush visuals in most games
You don't mention the resolution of the monitor. but I highly recommend searching for a Freesync one.
Assuming you mean 144hz at 1440p or below, this rig will be more than adequate I reckon. You may not hit 144 frames at all times at 1440p but I can't see it ducking below 60 fps.
Wow, decent build at a great price. I'll be basing my own off this, thanks!
In his description he says he's using an old laptop HDD as well as SSD. ;)
It's a decent budget set up alright, I'm looking to use the same CPU\GPU combo for a home built Steam box.