Scott, don't forget that my numbers are on a piped GT33. I see guys reporting much less on the stock muffler, for 19" props. All things being equal, it seems to me the pipe boost is about 1000 rpm over the stock muffler. But the Hatori canister is indicating intriguing numbers.
The IBEC has many advantages and weight reduction is one good one. But for an older guy like me, the safety aspects are most important. I've been preaching this to sport fliers for several years now but I swear they are deaf.
Back to Sungo for a moment, if you do get to play with the OS glow plug on the GT33, please report back with details....muffler versus pipe, type of gasoline and oil including ratio, props, etc
If premium gets more RPM than Avgas, then using premium with the Hatori muffler might be a better option. Start with that to get some numbers and go from there.