At risk of running off on a tangent, I'm curious about using straight bars for long distance road touring. I may be overestimating how long I can travel in a Tour-de-France stance, but I was inclined towards drop bars more as a way of dealing with our infamous wind, and not so much as a way of varying my hand holds.
Whatever you do, I suggest you decide on the bars before you buy the bike. Flat bars warrant a slightly longer top tube than drop bars. If you look at the Thorn sizing information, you will note that they sell frames that are not just sized by seat tube length, but also by top tube length.
And if you are doing a total re-think on bars, also consider the trekking bars, there are a small number of trekking bar fans in USA because of the many options for hand positions.
I think it is personal preference. I have seen a lot of bike tourists from continental Europe with flat bars, but in USA drop bars are the norm for touring bikes.
If you use bar end shifters, I have heard of some people that complain that their knees hit the shifters when they pedal out of the saddle. I do not stand on the pedals, my knees can't take that much stress but years ago when I did I never had a problem with my knees hitting anything. But I use bars of a proper width for my shoulder width and I do not pedal in a bowlegged fashion like I have seen some people pedal.
I used to use the drops on drop bars about 5 percent of the time and found them to be very uncomfortable. But after losing about 15 to 20 percent of my body weight (now about 170 to 175 pounds at 72.5 inches height) I find that riding on the drops of drop bars is much more comfortable now. Now I use the drops on my drop bars whenever I have a head wind or for fast downhills, probably about 20 to 25 percent of the time. Tops of my drop bars are about the same height as the top of my saddle, or depending on which bike maybe slightly lower by a cm or two.
When I was in Iceland, there were some pretty strong winds on a few days, I could not have imagined what it would be like without drop bars on a day with those strong headwinds.
But I tour with a friend that switched to bars that I think he calls bullhorns. They give him the ability to ride in a position very much like riding on the hoods with drop bars, but he has no drops for a more aero posture. But he is obese and I think he would have trouble riding on the drops. The attached photo shows his bike, it is the one on the left and is the one closest to the camera. He has used these bars for several years now, he is very happy with them. You can see he uses bar end shifters on those bars too.
I posted photos of my Sherpa above, but I have changed the bars to a different drop bar since those photos were taken. The second photo attached is of my new Sherpa bars. And a different handlebar bag too.