Tire pressure is important but when looking at models for our purchase last year I always compared the base weight with the gross combined weight rating. There were quite a few that after adding the weight of a couple of people, a full tank of fuel, and a tank of water they could barely carry a dozen eggs.
Weight was one of the reasons we decided on no slides and going with the E450 chassis. My 27Q will carry an additional 8,348 pounds of fuel, water, people, toad, and junk. I doubt I will ever come close to that. We tow a trailer with two Harleys and a canoe so thats around 2,000 pounds (towed weight). Still leaves me with over 6,000 pounds for us and everything else.
It's a 2006 (2005 chassis) and I have absolutely no issues with handling at any speed and it's all original equipment.
Looking at some of the longer models I'm sure the wheelbase on many is too short. Some look like you could jump on the rear bed and make the front wheels come off the ground.