I have the wider alloy rims on mine, it increases the width to 56". So far it doesn't feel tippy. I was nervous at first. I have had it drifting thru corners on gravel roads close to WFO (50ish) and felt completly in control.
As far as the AWD , I doubt if I will ever use it. It can be switched off and on. I'm not into mud and don't really like climbing hills (unless I'm at the sand dunes) As far as I'm concerned it would be nice to have the choice to order the machine with either 2wd or the awd.
There is a differential in the back so I'm not quite sure it's "locked" completly. I've been in cars with spools (basically a locked rearend) and know how they feel on pavement and the RZR doesn't feel that way.
In the next year or two I will be in the market for a mini buggy for the daughter .. mabye a two seater 150 or 250 for the girls to have fun on.