The school that I used to teach at switched from Abeka to Saxon Course 3 (8th grade). The students had a pretty rough time adjusting to the new layout. I did not teach either of them that year. The next year I taught both the 7th grade Abeka and the 8th grade Saxon, most of the class struggled but that was with everything, not just the math. Thinking about the woes of switching I somewhat tried to prepare the 7th graders for the book. I even did a few of the beginning lessons (of the 8th grade book) at the end of the year to give them a feel for the layout. That following year things didn’t go too bad.
I would recommend switching to the Saxon course 1 (6th grade) and then working your way up the grades. This would be easiest on the students. I don’t know anything about the elementary grades. For the high school curriculum Dr. Shormann has a rant about 3rd vs 4th edition here. I think he is also working on a curriculum that incorporates Geometry into Algebra I and II.