We had a 31 foot Keystone Springdale and then went to a Keystone Outback 298RE (Rear Living room), same as ktmrs (above), except it had a closet slide in the bed room.
In my opinion, going from the 31 foot to the 35 foot showed no difference. They towed the same, both took the same campsites (length), and backing was just about the same, after a couple attempts and got comfortable, never a problem again.
Now, if storage is the reason to stay 30 feet or under, I understand. But if for some reason there is a difference in 4 or 5 feet... well ... there really isn't. Once you hit 30 feet, it's all about the same, might as well go for the gold and get the 40 footer.
Go to ThorIndustries.com and select the RV and drill down to each manufacturer. Click on the blue button near the bottom, "Meet the companies". You'll be blown away with what's out there, and who ThorIndustries children companies are.
Good luck!