It seems like the cases are pretty similar, but If someone had or had jumped through the SAAMI hoops 30+ years ago the 6.5 Redding and todays Creedmoor would still be pretty different. 30 years ago the redding would have been twisted and throated for 120's and would have been the same as the 260 was when Remington legitimized it. What Hornady did was get the the OAL, throat and twist in the creedmoor figured out.
The 260 Remington's introduction was poorly designed and managed. It seems as though every time Remington made a decision regarding the 260, they made the wrong decision. I think that the 260 Remington would have been much more successful if Remington had done the following upon its introduction in 1997:
1. Standardized a 1-8" ROT instead of a 1-9" ROT.
2. Offered the 260 in their most popular rifle styles, the 700 ADL and 700 BDL.
3. Offered 3 standard priced factory loads in 100, 120, and 140 grains that were loaded to maximize their velocity potential.
4. Pushed the 260 into the market via a matte/synthetic 700 ADL sold through high volume retailers, like Wal-Mart, that was priced between $300 and $350.
5. To support #4, insure that 260 ammunition was on those shelves when the rifles hit the racks and that it was priced comparable to the 243, 270, 308, and 30-06.
Don't forget that the 6.5 Creedmoor designers had the benefit of seeing all of the 260's flaws and fixing them.