I just had an idea which might speed up the evolutionary process
significantly. After reading about parsimony pressure, I've chosen the
DoubleTournamentSelection which delivers a great performance improvement. In
my configuration I follow the manual and do a size-based selection first and
afterwards fitness is used as the criterion.
I'm not into detail of the ECJ framework but at which point of the pipeline
does ECJ compute the fitness? If it is directly computed after creating all
individuals it would evaluate the fitness of individuals which cannot be
selected because of their size. Thus it would be a good idea to evaluate the
fitness after selecting the individuals by size. Maybe you're already doing
that way but otherwise it could result in a speedup.