Yadda, yadda, yadda, after a lot of trial an error it looks like I got s3tc textures, and DX10, at 3840 x 2160 working. I screwed up initially by not checking that I extracted the DX10 renderer, and its separate folder with other files, into the Unreal system directory. It has to be aimed there.
I felt bad about downloading all the textures from that site you linked to, but the other links that were listed there were dead. Fast server though.
www.unrealtexture.com/Unreal/Website/Downloads/Textures/ExtremeEnd/StockUnreal/UnrealExtremeEnd.htm
Later I found what might be a different source,
www.moddb.com/games/unreal/downloads/s3tc-highend-texture-package, but that doesn't have the other uber textures offered at the other source. Edit: Weird, other textures might be larger?
Here's a link i found for a DX10 renderer that works with older Unreal games. it was mentioned in a GOG forum thread.
kentie.net/article/d3d10drv/
So I just had to change the renderer to the DX10 one by choosing the option to change renderers within the game, and then when it relaunches choosing DX10.
Within the folder is an nglide configurer. I launched it, and chose 3840 x 2160, but I might not have needed to do that as maybe the option for that resolution is under the in game preferences selector. Bleh, my head is spinning, just like nearly twenty years ago!
P.S. My Unreal Gold folder grew to over 4 GB in size.