Basically the same drive but supposeduly they upgraded some hardware, the only real change I see is the 4X +RW but the thing is there isn't any 4X DVD+RW media out.
I just got my 510A on monday and haven't had a chance to test it out that much yet, only some 2X DVD-R media I had left over from my old Pioneer DVR-104. I got it for $290 through a hookup, and I find it strange that for such an expensive drive they can't even include a single piece of DVD+RW or DVD-RW with the dive unlike every other manufacturer does with their retail packages.