Jhart, it sounds like you're getting good speed out of your Sport with standard fins. I don't have any comparative speed data for the Sport, but still think the answer might be yes. IMO, both STs and Turbos are more efficient compared with standard fins, and more so at higher speeds where standard fins seem to loose power or "mush out". In the Adventure and Oasis I get much better cruise speed with the Turbos. I think this rule would apply to any of the boats, though each boat has its own speed range for any particular individual.
I would buy the i12s for its portability, weight, excellent capacity and great stability, but not for speed. For me (with Turbos) it runs about 4..5 to 4.6 MPH on a one hour cruise, about 4 to 4.25 on extended cruise and 5.9 sprint (calm conditions without current or tide). You may find it to be faster or slower though, depending. In any event, its neither a slug or a rocket, but certainly not on the faster end of the Hobie speed spectrum!
PS: I called a friend who has a Sport and switched to Turbos last year. He said Turbos definitely improved his performance and he wouldn't go back to the standards.