I too was looking at a 1610D vs. 1810D about 4 years ago. They are very, very close in size. Nearly pulled the trigger on a 1610 but then I came across a 1720D. Again , the same size, but the XX20 denotes a few "luxury" features that are not available on the 1610.
The most noteable difference is that the powershift lever is located right next to the steering wheel on the right side of the console, which is conveinently close to the loader controls. This really speeds up loader work and allows me easier entry/exit when I'm wearing my big pack boots and more room , as mentioned earlier.
In the end I bought a 1820D as it is the most HP in that size machine. After that, they step up in weight, size, & tire size.
I also have a Koyker loader and remove / install it almost weekly. At first it was kind of a pain , until I made a few changes to my procedure. I now park the loader on a flat , hard, and level surface. I also extended the loader hydrualic lines (supply & return)by about 24". This allows me to hook up the loader controls before I connect the loader to the tractor so that I can use the loader controls to make small adjustments to get everything lined up. With this procedure, an open end wrench, and a big drift I can install the loader in under 3 minutes, and remove it in less time than that. I believe flat, hard, and level is the key to the whole operation.
I'm glad I took the extra time in looking before I bought, I could have lived with most of the machines I looked at, but its a joy to operate one that really works for my needs.