I'd say 4x4 UTV/sxs things are a complete non starter on extreme ground, but it depends wot u call extreme ground.
Most farmers/keepers i know who have 1 say they replace a pick up rather than a quad and most still have there quads for stock work (utv's to numb) or for wet weather soft ground, or steep ground
It all depends on ur ground thou and wot u want to do with it. They are a lot wider a lot heavier, lot less maneorverable and if u get stuck u will need a tractor no chance of lifting/digging it out urself
Use 1 on 1 shoot as a game cart and bloody handy but it does mark fields when wet,(quad and trailer would probably be as handy if not handier ) had the crew cab 1 day too to ferry the guns about was quality piece of kit got 5 guns in it plus 3 in other normal polaris but was marking the fields as quite wet wknd (the landy gun bus was brooken down, again!!)
U can get windscreens or roofs for ur quad, i would not be without my windscreen/roof now on the quad throu winter makes a massive difference when ur on it all day
The Polaris 6x6's are excellent thou and will go a lot of places u'd go with an argo, in some cases go more places as won't get bellied the same in snow/ruts, ride totally different to the 4x4's on steep or boggy ground and the lower ground pressure makes a massive difference, 1 moor i go to got rid of argo's for them. Cheap compared to an argo.
The other option is an off road trailer behind ur quad, TFM engineering make a decent hill trailer that comes apart so cn be stored under the quad in the road trailers, decent bit of kit