Any caliber in an AR10 platform is going to be a comprimise with other than a 308 based cartridge. All the odd ball caliber riifles are inherently finiky and even the 260's and 243's can be , form powder burn rates and how it affects the port pressure of the gun .

To get the most out a 6.5/284 it really needs to be a long action gun . To take advantage of the case capacity and the high BC bullets it needs to be loaded long . When loaded to SAMMI OAL it will not reach the 3000fps range with 140's , the highest BC's are in this weight range .

If the high BC bullets are not going to be used it makes no sense to go with a hot rod cartridge that will shorten barrel life and increase your loading head aches . If varmint bullets are going to be used I'd get a 243 and be done with it .

The wind drift is really the more important number to compare since the bullet path is a known value and is compensated for with the scope before the shot .