In my short action 6.5-284 I gain 250 fps over the 260.
I'd sure like to compare velocities of several bullet weights..
in a 260, I can run 140s at 2750 to 2850 depending upon powder...
so can your 6.5 x 284 loads beat that by 250 fps?
if so, then that is impressive..
In my testing, I didn't see that much of an increase on all the loads I tried..\
If the 6.5 x 284 did beat the 260, it was only by about 50 fps..
I had the good fortune of being able to borrow a friends rifle for testing against my 260, when I was looking to build a long range 6.5 on a Model 70 action..