The gap did provide a bit of a buffer, but I nonetheless did not care for the transition. While the systems were quite different, I believe it was more the difference in the teacher quality that had the largest impact. I was fortunate to go to a small, exceptional Montessori school before such things became ridiculously expensive, while the public school, although it had a few very good teachers, also had some very marginal ones (basically, tenured and terrible).
If the quality of teaching is similar, then I expect the transition would have been much easier. As others have noted, shop around since the teaching quality, rather than the teaching structure, is ultimately what was the starkest change for me.