I studied various factors when putting together my computer based handicapping system and one of those was the break between races. Not taking into account any specifics like distance of the races, age of the horses, etc it was hard to draw any conclusions which was the "best" break between races. When averaged out even long breaks of several weeks didn't seem to produce any great advantage or disadvantage - with one exception.
If a horse had run within the last 7 days ON AVERAGE it had a slight advantage over other horses.
KV