i just finished building in the pro 5, looking at pictures the R5 seems practically identical. what i am looking for in the future that i dont think i would find in the r5 is a clean, first party GPU support bracket (i am really gunning for that and the master case has the potential).
the problem i have had with the pro 5 is that they gave me so many gosh darn fans but only molex power adapters and no fan hub or splitter to make all the fans bios controlled. this is a small bother but i am working through it with little difficulty.
R5 has the potential to be quieter but honestly once i have the right fans installed the pro 5 is good enough. they padded the PSU support so the loudest thing i deal with is fans at idle or inductor whine when under graphics load. i dont think it is doing anything to be quieter but its not part of the problem by any stretch.
my last case was the core v21 by thermal-take (good riddance) which by comparison this is the same steel material but actually machined precisely and well fit. i never knew captive thumb screws where so great either.
long story short i am biased toward the pro 5. it looks like the R5 has a different aesthetic and a focus on noise control and by contrast the pro 5 is larger(fact check?) with a focus on being able to do whatever you want and have interchangeable parts for the future.