Contributory Parent Visa - Still Sparkling!!! - Part 4 - Page 71 : British Expat Discussion Forum.
I don't think there is any difference in spead of processing.
A few things to beware: You can only apply for an onshore CPV if at least one of you (you or your OH) are old enough to be eligible for an Aged CPV (ie, of Oz pensionable age), if you do not enter Australia "with the intention of applying for a CPV", and if the visa you have (eg, Tourist) has no "No Further Stay" restriction on it.
You'll find out a lot more by reading here and DIAC's Booklet 3 – Parent Migration (downloadable).
Good luck, Mike