yeah the loops can be a bit of a hit & miss affair,im constantly making adjustments with the jog wheel, although i think alot of that can be maybe down to the beatgrids slightly out,most of my tracks beatgrids will rarely match all way through no matter what mode or what fw update they have been analysed by even manually adjusted to,usually have to make a manual adjustment live on the cdj,now im going off on one sorry!.There shouldnt be any negative difference with quantize on than off.with quantize on it snaps to nearest mark on the beatgrid & with it off anyware only thing i can think of.i cant help with any comparison to 900 functions as ive never used them.