Certainly if you are looking to step up to more class 5 you will need a bigger volume boat than the fun series. That being said I have run my Superfun down Gore but did kinda feel like I was getting my butt kicked & only did it once
I do recommend the fun series for anyone regardless of their Actual ability. They are a great well rounded boat & do everything you want (other than creeking) in a single boat at a adequate performance level. They also have a great manufacturer backing it up.
Careful about biting off too much too soon. We are all better boaters in our own mind