I personally have not tested the 3D client on IDOC.
The client its self is more resource hungry than the 2D client for obvious reasons.
From a netcode perspective, the communications between the clients are 'fairly' similar so performance issues would stem back to your computer specifications.
The 2D client is preferred by most veteran Ultima Online players for aesthetics and performance.
If you are talking about the more recent 3D client, then expect issues with playing on IDOC.
IDOC currently only supports Ultima Online Client 7.0.10.x (the base installation of Mondain's Legacy).
If you are able to run the KR client, you can expect to see a lot of cliloc errors and also 'invisible walls'.
At this point in time we are keeping things simple so people can essentially download and play.
In the future we may look to moving towards the newer client, but one step at a time.
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