Up to what size resolution monitor will work well with a mid 2012 Mac pro retina 15" with an Intel 4000 graphics card?

[paul31008]

Looking for a monitor that will work well with a Mac 2012 pro retina and future laps when this one needs to be replaced.

 

[Lutfij]

Read this.
Essentially, you didn't mention the processor on your Mac. Though this that the maximum supported is 2880x1800.