One way to establish your limiting magnitude is to go and get the latest edition of StarWare by Phil Harrington. He has a map of the southern cross and from memory they go down to mag 6 or something. Using that map I determined my suburban sky to have a mag limit of between 5.4 (summer) and 5.6 (highly transparent winter nights). Good enough to bag mag 10 and brighter galaxies
Hope that helps.
Darren