Someone finally made a D3D8 to D3D9 wrapper for FFXI (apparently I can't post the link here, just do a google search for "FFXI D3D9 proxy")
Basically this redirects D3D8 calls to their D3D9 equivalents and can significantly improve performance especially on Windows 7 and later. You just put the D3D8.dll in FFXI's directory which will be the first version of that DLL it sees so it loads that instead of the real D3D8.dll from the windows system directory and then FFXI's D3D8 calls get translated into D3D9 calls.
Things I've noticed with this is that, FSAA now works, but slows down significantly with full shadows (literal slideshow with full shadows enabled). However if I use the old method of doubling the background size in FFXI's config for full scene supersampling, full shadows now have almost no performance hit at all where before there was a noticeable framerate drop. It also solved most of the z-fighting errors I was having in Windows 10.
SE needs to just patch the D3D9 code from the 360 version into the PC version and be done with it. They already did this with Xinput support last year. (the 360 uses DirectX 9 so the 360 version had to have been using D3D9)
Edited, Oct 1st 2017 5:48pm by Lobivopis