Most implement advertisments will have an engine size necessary to pull the implement. Probably based on wieght, and I've never seen one that recommends less than 500cc.
If I was in the market for a new DRV I'd look at the Yamaha Grizzly. I'm not sure of the engine size, I think it is close to 700cc, but it is fuel injected with some sort of power steering. I'm hoping they put that engine and steering in the Rhino. Then it will be time to trade.
I'm not really up on the ATV market anymore. There may be other machines out there with better features than the Griz, I just know I liked mine when I had one.
Oh yeah, one other thing, I'd for sure get a liquid cooled engine. Pulling implements at slow speeds is gonna build up heat quick. Again, I don't know, maybe all 500cc+ engines are liquid cooled.
The 'Bonker