Skyrim uses physical models for the terrain. The terrain is imported as a heightmap and converted to models in the creation kit and given LOD replacements so the actual terrain in the game world has to conform to this lower size because of the game engines restriction on number of vertices per model. You could see that if you used Nifscope and opened a terrain file. It is a model not a heightmap.
First I don’t have a lot of experience with UE I worked with CK and BWT so I can only speak from past experience on these engines. With BWT the tile size was set at 100 meters per chunk the number of chunks loading and unloading as one moves is rather smooth as long as the amount of unique models was kept low. If the number of unique models became to much for background loading then there would be spikes and video stutter. Try to minimize this by keeping a balance required spreading the models across several chunks.
I would suggest testing 505 or 1009 tiles. I think 2017 is to large but that is just my opinion. Lower setting like 127 or 255 may start to degrade performance since there will be more drive access. If you use a lot of unique models then maybe going lower setting would be wise so there is not a big spike.