In a nutshell... The change to two groups - one faster - didn't work.
As I alluded to in my last post, I have a range of math abilities in each of my precalculus classes. I have 2-3 students who could easily be successful in an advanced calculus class this year alongside students who would be better served by a normal precalculus class. (Groups in-between could include an advanced precalculus class and a normal calculus class.)
The idea was to see if I couldn't serve two groups' needs in one class, and I discovered that it just didn't work. I found that, within a 40-minute class, there wasn't enough time for me to be available for both, and I felt that my attempt to split time (quite unevenly) resulted in less quality time with both.
Live and learn.
Things have settled down quite a bit this semester, however. I've discovered that homework of 6 problems/night is close to ideal for my students and the time we have, and, thanks to some construction changes that took place over our break, I now have plenty of chalkboard space on which to display problems. The students know that they'll be presenting every other day, so they come to class prepared to get started.
Quite a learning process for me. I'm lucky to have such great students.