I really liked how DTEK50 felt in terms of performance. PRIV and DTEK60 are faster (i feel) from a launching apps perspective. I did not spend a ton of time on DTEK50, but it is an upgrade from the DTEK50. However, if you are not trying to play games or do anything crazy like heavy editting videos, images etc. you will probably not see the performance increase from DTEK60.
it really does depend on what you are doing on the phone ...or want to be doing with your phone.