Well, technically... 64bit has less rounding errors (the whole point of it), which means less noise (right?)... which means, someone with golden ears and great system/room COULD hear it.You cannot hear the difference between 32bit and 64bit summing
In my book, examples for golden ears are Hans Zimmer and Eric Persing of which both are claiming PT sounds the best, Logic the worst. I tried comparing Cubase and PT HD Native on my Win machine, couldn't hear any difference... maybe PT on Mac sounds better? :D ... maybe PT with 32bit floating point math sounds the same as Cubase and the old PT with fixed point actually sounded better.. i dunno and I certainly haven't done any meaningful testing, but how I look at this is - I believe HZ, Eric and others until I prove myself they are wrong.