I have towed all sorts of trailers with all sorts of weights with pickups over the decades. I've towed an enormous amount with a 1/2 ton pickup and got by with it. That being said, I have changed my ways and have been converted to use an "appropriate" sized truck and trailer.
Heck, I used to think that I should have no problem hauling however much firewood would fit in the bed of my pickup. Nevermind that it was a 1/2 ton with a full sized long bed. Upon closer examination, I found that I was severely overloading my truck. Fortunately I never paid the price.
As a lot of people have mentioned, braking is an important factor. Also, the ability to actually handle the load under less than ideal conditions should be a factor. For example, if a little kid runs out in front of me chasing a ball, I want to not only be able to stop my load, but also be able to immediately make whatever directional changes necessary to avoid a disaster. In a case like I mentioned, I technically wouldn't be at fault, but I'd have to live with the memory for the rest of my life.
Anyway, I've found that for the amount I tow, a 50hp tractor with a loader and implements, a 1 ton diesel dually is the proper equipment. Also, in an earlier thread, I told of how I also found out (very nearly the hard way) that you should never use ratcheting straps to hold that kind of equipment on your trailer. Yet another thing I found; using up every bit of the "rated" weight carrying capacity of your trailer makes the trailer handle a bit worse than I care to tow. Remember, the rated "limit" is just that; the maximum amount the trailer will handle under ideal situations. The same goes for the maximum towing rating of a pickup. That figure is based on all conditions being ideal. In the real world, things are not always ideal.
I feel much safer when I am not pushing the limits on my trailer or with my truck. For what you are wanting to do, I'd highly recommend a 1 ton pickup. That way, you shouldn't be pushing the limits of everything. It leaves a little room for error or less than absolutely ideal conditions. But, that is just my opinion. /forums/images/graemlins/tongue.gif