One factor that may/may not have an influence on your decision is if your current Rem700aid a long or short action.
I am about 3 weeks away from receiving my .260. I have also been reloading for my buddy who has a 6.5creedmoor. So my opinions are based off too many hours on quickload, countless hours of research, and asking experienced shooters opinions for the .260, and actual experience with reloading/shooting the 6.5CM. So.... I think the .260 has greater potential, but the 6.5CM is probably an "easier" cartridge to load to the cartridges max potential. Simply put, they are almost identical balistically and you won't go wrong either. As stated above, if your newer to reloading though, I would say hands down go with the 6.5CM.