I dont know if its just me...even if I run a huge resolution, I dont see much of a difference. Well, its a bigger res..but... Ie. 640x480 on an original Amiga vs switching to a bigger resolution made everything smaller and gave alot of desktop real-estate like if you switched to interlaced or using a cybergraphix card and jumping to a different res.
As far as I remember MorphOS supports resolutions up to 2560x1600 with dual-dvi mode.
This requires some better GFX card. AFAIR Raden 9600 and better.
MorphOS itself should be able to deal with 4k screens, but 4k displays are currently not possible due the lack of more advanced graphic cards able to deal with it.