On Redshift it should take 5 min.
Yeah right* - I doubt it if you want the same image quality. Whenever I've tried GPU engines, they're fast when they're cutting corners, but once you crank up the samples etc to get an equivalent image quality (esp on glass etc) then the render times get a LOT longer. 5k sounds like a still image - just send it to a farm for the final.
*Not saying it wouldnt be quicker tho'
I'm not going to make comparisons here because I find it unpleasant. But GPU handles it in seconds, the only downside I see is still the accuracy in calculating shadows, but for those who don't work with architecture it doesn't make the slightest difference. What I love most about Corona is its usability, a team that strives to develop something that makes the user's life easier. This you make sure no other renderer has.