I have a 25 Tohastu on my 4 metre Qunnie, it has had the restricter plate taken out of the carbie and is the same as a 30.
Full of gear and live bait tank full, two up, does 30 knots on the sounder - sounders can be notoruiosly wrong though.
This is the second Tahastu, basic, built well and have never had a problem - touch wood.
A mate of mine in Townsville ran a hire boat business and he used Tohastus, as you could imagine life for those motors were terrible yet they kept going. In fact I have seen someone wear a prop away over a weekend.