FWIW, having done a few crossings myself, I'll add my 2 cents. My view is that all production boats rated CE for offshore use are bluewater capable. But and it is a big but, the weakness is the crew. When faced with high winds, ugly seas, some boats are capable of keeping the crew in better shape than others. After 48 hours of high winds and disturbed seas, some boats beat up the crew - fatigue leads to mistakes or even a distress call "get me the hell off this damn boat".
Racing boats - the Volvo types for example, have trained pros - very fit athletes whose endurance is far greater than mine. Speed is all and concerns of comfort and crew rest under tough conditions are secondary.
So to end this, a true blue-water yacht is one which in addition to the criteria posted above is one which has a kindly motion designed to minimize crew fatigue under storm conditions. Of course this also implies a sail plan and equipment which allows mere mortals to manage the boat under challenging conditions. I think this explains why some of the older designs with narrow hulls, fine ends, heavy construction etc are still popular. Comfort in a gale has a higher priority than sheer speed.