I did that exact loop in September of 2014, Fantastic trip!  You should have good water levels in May.....Let me check my maps and log and I can give you more details....We traveled to Frost Lake the first day and spent two nights there, it is an absolutely beautiful lake with sand beaches.....lake trout and Northerns....We split the river into two days and overnight end on Bologna which is only a couple of hours from Frost lake.....We stocked up on water from Frost lake with a couple of dromedaries as the water on Bologna ,even after filtering is awful!   Day 2 on the river is a very long day, I think we had over 20 beaver dams to lift/drag over....very scenic though!  All in all a tremendous trip!

Mike