[ironmark]

I wouldn't worry about it too much. The seat poll doesn't do much good because everyone is different so just try to find a seat that works well for you and your wife. For what it is worth I use the HD leather low profile seat which works very well for me, but I don't ride two up much so it probably won't work good for the wife.
Most of us older people are not as fit as we would like to be, Father Time is not nice and he gives us lots of aches and pains.
You are only going to ride as long as it is comfortable for you and your wife (if she is with you) and it will depend on who needs a break first.
I can ride until it is time for some gas and I start looking for gas around 130 to 150 miles because I don't like running the tank too low and if you're not in a familiar area it is better to stop for gas sooner than later.
When you stop take as much time as you need, you're not on a iron butt run and if you are you're too old for those things anyways so stop.
The main thing I found to have extended ride time for me is to have footpegs mounted to the crash bars so I can move my legs into multiple positions. I mount the footpegs lower on the crash bars so I can rest my toes on the pegs and my heels on the floorboards doing this give me 3 or 4 positions to move my legs too, your wife options are more limited. I also removed my heel shifter so I have more room on the floorboards.
In general a 250 to 400 mile days is good if you're on a road trip figuring in stops for scenery and fuel. There are times that I am on a mission (I just got done with one) and I have done 550 to 700 in a day depending on the roads, but I didn't have any time to stop and enjoy some sights and take some pics.
Bottom line is take your time and enjoy the ride, time flies by too fast anyways

 

[ironmark]

Great responses so far. I've noticed some trends here and on some other seat-threads:

Highway pegs - the ability to move your legs around is key to allowing the blood to flow in areas that might not be getting it enough. There are highway pegs on my bike (were there when I bought) but they are too far away. I'm going to need to buy some extensions. The only problem I have with highway pegs is that I've had them before and I typically almost never use them because I don't generally ride long enough to need to use them.

Get the adjustable footpeg mounts, I got mine from Harley but I think there are other sources for them. The mounts are a little pricey but they are worth it IMO.