Charles, as to velocity I get my information from published data. Published data has the 284 based cartridge faster than the 06 based one. Both my 6.5 X 284's are running much hotter than published data and I have never had any luck pushing anything based on an 06 case up much in pressure.
As to accuracy, 20% of the 1k guns I am seeing at the present are 6.5 X 284. I have never seen a 6.5-06 in a 1k match. I am guessing there is probably a reason for that.