I've got a buddy that's got both, and with either you can expect fast growth, I think 8-10 ft in the first year (someone correct me if I'm wrong) adult sizes burms likely won't go past 16-17 ft, retics yeah upper 20s is possible but 20-24 I think is more likely. His retic is only about 8 ft right now... but one of his burms is around 16 and she eats a rabbit every 2 weeks