That I am very aware of - as this makes my 5th retic. They are often very alert, curious species - always on the move.Retics are vastly different from every other species.
I guess it all depends on your definition of big, and fast. While pure dwarfs may still get to 12-16 feet long. Generally the high percentage(75+%) SD won't get much larger than a pure Super dwarf (6-9 feet), maybe 10-12 feet for heavily fed females.They get big fast no matter what percentage of SD/Dwarf they are.
In his case - it also helps that his parents and grandparents where all in the 6-9 foot range.