Originally posted by ElJamoquio how vivid colors are and how sharp the image is
All this is true. As the ISO ramps, the DR falls away, of course. DxO rate the K-5 optimum image quality ceiling at ISO 1200, and it's clear that progressively from there things will degrade.
I guess it is just a matter of taste and usage scenarios - gallery quality fine art prints of landscape scenes, or A4 or A3 prints of wild musicians at rock and roll gigs. Noise, grain and lower DR hardly matter for the latter, but they matter a lot for the former.
It's surprising (and rewarding sometimes) that as long as an image is in-focus sharp and/or has some strong feature elements to draw the eye, it can survive the perceptual journey to even the highest ISO very well. The viewer often simply won't notice or care about any technical defects, as long as they see a message or find something that engages the eye. Hence Lomography, Instagram etc.