Going 4K depends on a few things.
- Can you really use that resolution?
- Do you have a DisplayPort 1.2 output? (this is important)
The second bit is really important, because most 4K monitors are actually two panels and they rely on DisplayPort's multistreaming protocol to do 60Hz refresh. As for quality, I know Dell has a 4K monitor that is 99% Adobe RGB and 100% sRGB and they're usually good now about calibrating it for out-of-box use. It's also $3000.
So it's really up to you. :B
But if you routinely work on pictures over 8MP, it might be nice to see the entire picture at 100% zoom.