welcome to the board cperso
another aussie just what we need here lol
a 1/4 inch peep should be big enough altho some say they are too big but the do let more light through in low light conditions.
Personally I have gone away from using a peep sight to a hind sight which so far works great.
The peep will also give you another anchor point plus will give more accuracy
if you can shoot a 12.5 to 15 cm group that should put you right in the kill zone