I may be generalizing, but I think once you get over 40' you are getting 1-1/2 bathrooms. If that's not important to you, there isn't a lot of gain going over 40', and there are even 40' and under with 1-1/2 baths but it starts to get tight.
Tag axles track in wind better I have heard, but that's not why they are there. They are there to overcome the load on the rear. If you have 40' and under, the manufacturer may not have installed a tag, but still may be a well handling coach.
In 2013, we were the longest Winnebago made (43'6") and we struggle in some places, but when I drop the Jeep I only have to park 43.5 feet. In most 5ers you are parking 60' or more while the truck is hooked up.
We agree with what Don says above.