4k is lovely I had a hard time swapping but on a desk 40" is way to big to sit in front of, bring on 32" 4K IPS 120hz or 2160p Ultrawide. Out of them 2 the X34 all day long. It fills your view wonderfully while gaming.
If my comment is doesn't convince you well 4k without gsync is a massive massive no no unless your running 2X TX's
You used a 40" on a des?
Not too big at all