I have no personal experience with the Ultrapower upgrade, but if Ed does not see this, i will email him. He added the Ultrapower to his Dolphin and can give you good feedback on its effectiveness.
I just bought an '05 Sea Breeze LX 8375 on the W-24 chassis, and see no reason for performance upgrades at this time. If yours is like mone, it has dual exhaust, which helps in the performance. Not sure how much Ultrapower, or Banks Systems would help. I know the Banks System increases power and torque, but not sure if it does enough with the W-24 to warrant the expense.
Before you spend the money, wait for the feedback.