Depends on several things including elevation and heat, nitro content and pipe tuning. For example, the OS6b carb and pipe combination on my TT36 definitely adds power (while drinking way more fuel).

Unless you're flying aerobatics, you don't want -9 degrees or you're one twitch from a boom strike!

In normal (hover) mode I fly -4 to +9 but I set up my students with -2 to prevent them from slammling the heli down but giving them enough to conquer the gusty wind 'zoom'. When they start looping & rolling, I drop negative to -6. -9 comes in when you want to climb away inverted (panic out when learning inverted ).

Idle 1 & 2 I set to +/-9 with zero at center stick. For my students entering forward flight, I set all modes to +9/-4 and bump their head speed while adding throttle below hover in both idle 1 & 2 (they often click through accidentally).

Hope this helps.