The 30-06 family of cases have features that make them a good choice for improving- and the 280 does it nicely- and comes out with a very good end product. It is the only improved cartridge (that I am aware of) you can buy off the shelf and locally has many more ammo choices that the regular 280.

As far as the sudden found speed of the 6.5 CM..... it is over pressure-- WAY overpressure. Quality brass came out that was able to handle/hide the results of that pressure- some powder developments as well-

A company with the equipment to test pressure tested the loads they found on the internet -- duplicating the brass/primer/powder/bullet and found that many of the "safe" loads are well in the 70,000 psi (and higher).