Its hard to know for sure. Maybe 10.5D would be more comparable to 10E, but there is no exact science involved, especially across different lasts. How do the Indys fit in terms of length, width of the heel, width of the forefoot? Snug or roomy in any of those places? Not uncomfortably so, but if you were able to change the dimensions a little, are there any places that you would want it more or less snug?
If your looking to buy another pair and haven't settled on a specific model yet, check out some shell cordovan, if you are open to that kind of thing.
My 10E Indys are not too snug. My heels, especially the right heel, are no way snug. The forefeet are just perfect.
My left foot is much bigger in the heel area, don't know why, freak of nature thing going on with my feet.
I would say, my right foot could fit in a 10D with ease, the left... I don't know, forefeet surely, heel... IDK. Depends a little bit on how these will stretch in the width.
The Trubalance last usually is a little bit more generous in the width than the Barrie last. So if your Indy boot is snug in size 10E, I definitely wouldn't recommend going with a 10D on the Barrie. 10E on the Barrie would probably work better for you. Hope that helps.
Hm. Too bad, if you were right. 509,- $ is a very good price. What a shame there's only a 10D left, no 10E. Returning them is no option, I'm from Germany and would have these boots sent to a friends son in the US. My friend is going to visit her son in a few weeks and will bring them back to Germany for me. I will try them on when they're already in Germany.
First world problems...