Hm... sugar beet wine?
Interesting red color, I wonder if that gives it antioxident powers?
;-)
I would think that rock sugar would slow the fermentation down considerably, but you're have to kill the yeast to stop it anyway. Your OG and FG would be un-related, because you would have sugars being constantly released -- you would not have a hard reference point for the OG. I think that your ABV would also be lower as you would probably want to quash the yeast so you would bottle it, or you'd wind up having a much longer fermentation to get all of the sugars converted.
Hey, I wonder if that would yield an "aged while fermented" cider? Probably not, as only part of the cider would be aging at any given point in time, and none of it would be aged the same amount at the other parts. I am getting dizzy.
If you're looking for information on final flavor differences, I can't help you there, as I'm still fermenting my first batch(es).
If you're looking for sweeter finish, I think the two options are, stop the fermentation sooner (lower ABV and you have a kill off the yeast) or follow through to final ABV where the yeast start to die out naturally, and then back sweeten.
All of this is supposition. :-D