if you have no power limits where you are, i would avoid .177. you can detune a .22 to lower fps if you want it quieter, and it will be actually quieter and shotcount will be higher at the same power level (17-18fpe) than a .177
there is not much to detune on a .177, i think the powerwheel is any good practically for larger calibers, using the same logic.
Giles was saying in his videos that he had a ST in .177 and a ST in .22 and the .177 would not group that tight, but it may have been only a faulty barrel. i think it was not a streamline but other model but still i think it does not matter.