From reloading manuals, the velocity advantage of the 270 is more significant than the BC advantage of the 6.5 CM.
For example:
From Nosler
6.5 CM - 140 AB, max vel 2733, bc .509, windage @ 1000 yds = 90.7"
270 Win - 150 AB, max vel 2918, bc .500, windage @ 1000 = 84.3"
6.5 CM - 150 ABLR, max vel 2725, bc .634, windage @ 1000 yds = 67.9"
270 Win - 150 ABLR, max vel 2918, bc .591, windage @ 1000 yds = 67.1"
From Barnes
6.5 CM - 127 LRX, max vel 2883, bc .468, windage @ 1000 yds = 94.1"
270 Win - 129 LRX, max vel 3211, bc .463, windage @ 1000 yds = 81.3"
Link to these trajectories on Shooterscalculator.com
Wind drift is also the closest quality that the 6.5 is to the 270. Drops are even more significant. At 1000 yds, the 6.5 is dropping a full 1-2 mils more than the 270 between the above matchups.