JAR-OPS 1 divides performance categories for public transport into 3 groups : A, B & C.
Your twin piston will come under Group B or Group C depending on its max take-off mass and number of passenger seats - but most likely B...
Group B: propeller driven aeroplanes with a maximum approved passenger seating configuration of 9 or less AND a maximum take-off mass of 5700 kg or less.
Group C: aeroplanes powered by reciprocating engines with a maximum approved seating configuration of more than 9 OR a maximum take-off mass exceeding 5700 kg.
If you'd like the full JAR-OPS perf requirements (gradients/speeds/configs/blah blah), email me and I'll TRY and dig them out for you