Regardless of brand-
1. If you are detecting in the VIC GT, where there are plenty of trees, quite a few hills etc, then power is not really an issue as UHF is line of sight. A 1W handheld would suffice as getting to the top of a hill they will still get out several kms and in that area you are never very far from anyone.
However if you are talking about the open plains of WA, then the more power the better, i.e. 5W (legal max).
2. If your Coms are for convoy, or for coms to a detecting buddy close by then a 1/2 or 1W each is plenty. If its for emergency further away then 5W is better.
I have an 80ch 5W in car rig which is Uniden with a roof mounted antenna for max range when driving. I have an 80ch 5W handheld Uniden for max range when on foot.
I also have (from many years ago) 2 x 40ch 1W GME handhelds, originally bought for me to have coms to my wife at the rear of the caravan whilst I am reversing as power is not an issue at close proximity.
FYI The government has rescinded its plan to phase out 40ch and make them illegal to use. (I think that was slated for mid this year) The old 40ch frequency transceivers will coexist with the recently introduced 80ch rigs. For those not informed - The first 40 channels of an 80 ch rig are the same as the older 40 ch rigs and will talk to each other in both simplex and duplex modes. The sound may be distorted between the 2, but will still work.
40 ch is called wide band, 80 ch is called narrow band. The reason is in simple terms that ch 41 thru 80 slot between ch 1 thru 40 roughly midway ie ch 60 sits between ch 20 and 21 re frequency.
The only downside of older 40ch rigs is they won't receive or transmit ch 41-80 if others use them. Also cheaper 40ch rigs with lower quality filters or frequency lock may pick up distortion from 80ch transmissions.
The brands to look at are Uniden, GME, Icom or Oricom (there are others) do a Google for reviews once you decide on power.