EDIT: wow this got long!

John. Some more of my bike thoughts.

You said earlier that you want a totally upright position with no forward angle at all. If you were to experiment I think you would find this is not comfortable for longer rides (centuries) because this puts all the weight of your torso on your spinal column and seat. A slight forward lean would allow you to put a small amount of weight on your hands, without putting you uncomfortably far forward as you have been.

If you want to do an experiment to prove this, try sitting bolt upright vertical in your chair. Easy. Now do it for five hours (joking, of course). Within a minute or so, you'll want to lean somewhere. You could lean back if your chair has a back. Or you could put your arms on the desk in front of you, or your knees, and put some weight on them, relieving your back. That is what you'll want to be able to do on your bicycle on a longer ride.

Also, a vertical seating position is of course aerodynamically unfavorable. There is a compromise between aerodynamic efficiency and a comfortable seating position, and each person must choose the correct compromise for their purposes and preferences. Your current set up seems too far toward the efficiency extreme, with not enough comfort. I'm concerned that if you go for a bolt upright position, you'll quickly realize that you've swung too far toward the opposite extreme, and are still unhappy.

You should be able to find a seating position that keeps you comfortable on long rides that is not bolt upright, thus saving some efficiency. That is your ideal compromise. I would be very surprised if you're not comfortable with even a small angle. But, like DX-MAN says, no one can tell you where that ideal compromise (niche-of-joy) is. You'll have to experiment (test ride).

Another key thing for long distance comfort can be multiple hand positions. This is why drop handlebars are great. You can get in the drops for efficiency. But if your back starts to ache, or your wrists/elbows are tired of supporting your weight, you can get on the hoods or the bar-tops. Basically it allows you to shift weight to different joints/muscles, so when you get tired of one position, you've got a couple others to switch to.

I looked at the Trek 7.7 FX you mentioned. In case you do still want bolt upright, those handlebars won't get you there. You would need a ton more rise and/or swept back handlebars of some sort.

As I said, I don't think you'll actually want that, long term. But I think you will benefit from drop handlebars because of the flexibility/versatility they offer. On the trek you would have to change to drops, but then you would have to get new brake levers and shifters, since the bars on there now are the "mountain" diameter and not the "road" diameter. Such a conversion would quickly become very expensive. Hardly desirable especially since the MSRP on the bike is near $2,000. If you want drops (and I think you do if you want to do centuries) get a bike that comes with them.

Finally, don't get sucked into thinking you have to choose between a bike that is comfortable and a bike that is efficient. You do have to find the compromise, but you should be able to find one that is very comfortable for everyday riding and still efficient enough for you to do centuries in reasonable time and keep up with friends. The bicycle industry tends to go to extremes... mountain bikes, road bikes, comfort/hybrid/bike-path, touring bikes... with relatively few examples of truly versatile and flexible bikes with plenty of comfort and efficiency for the long haul. But those bikes are out there for you. Salsa Casserole etc.

And I still urge you to test ride before buying anything else. Test ride a variety of styles and sizes. Unfortunately you can't ride em for 100 miles, but you can still learn a lot from just riding down the block. Don't hesitate to visit multiple stores if you have to in order to test ride all the bikes you want to try.