The E and G stands for the size rocket engine used in the event. E is bigger than most model rocket engines, G is the very biggest.
Superroc Altitude is scored by multiplying the altitude by the length of the model. You don't need to recover the model to win the event. To get a record you need to recover the model. My nephew Andy both won the event and recovered the model for a new B Division (14-18 year old) record.
Bumbling Brothers Flying Circus did not do quite as well, but did pick up a respectable 3rd place in the G powered event.