Here is the way i look at it. Unless you are going to go with something with less recoil for a reason, the performance difference with any of the 6mm rounds isn't really a significant difference. to me the 6mm rounds really comes down to recoil management and not performance advantage.
I have a 6.5 PRC, and just got a 28" barrel for a better mile shooting rifle. I made the choice to invest my money into a 6.5 PRC, my brother invested in a 7mm WSM with a 30" long barrel for the same purpose. It really is a tough choice between the 7mm WSM and the 6.5 PRC with (IMO) the advantage in performance to the 7mm WSM with a decent recoil penalty.

I would keep the 6.5 Creedmoor and get a 7mm PRC or 6.5 PRC for the longer range shots. I like to shoot both my 6.5 PRC and 6.5 Creedmoor and love having both. there is a definite advantage to the PRC. i am at 2840 FPS with my 6.5 Creedmoor with a 26" barrel and 140 ELD-M. with my 26" 6.5 PRC i am at 3050 with 147 ELD-M and 145 Match Burners. That is a pretty significant performance gain from the 6.5 Creedmoor.
I am hoping for 3150 with the 145 match burners or 3100 with 153 A Tips with a longer barrel, better brass, and trying out a few different powders. That should be the ticket for me.