I've been using dgVoodoo3d the past I dunno 1 month or something, could be shorter. Ranked based on performance it looks like this:
#1 DirectX9 (make 0 difference if I were to use dgVoodoo3d)
Having the best performance out of all (High Refresh Rate Monitor 120Hz), allowing me to have 120fps on most of the time, while dipping to 80fps on the really though to render places like on outside of Bitfrost Tower. Discord Overlay natively supported on DirectX9. Using dgVoodoo3d DX12 on top of DX9 don't seem to give any benefits.
#2 DirectX7 wrapped in dgVoodoo3d DX12
The performance on dgVoodoo3d is somewhat better compared to DirectX7. There were places where I had hard time getting 120fps, but with the wrapper, I can get 120fps, although not always 120fps. For example: Main Office is giving me hard time getting 120fps, but with the wrapper I kinda get 120fps sometimes. dgVoodoo3d supports Discord Overlay. Reddit post I followed to do this:
https://www.reddit.com/r/RagnarokOnline/comments/u7a6yo/i_made_a_dgvoodooguide_for_ragnarok/
#3 DirectX7
Original Ragnarok Online experience. Reeally bad engine compared to other versions. I never get 120fps on Prontera nor Main Office. But the goodside is lower CPU usage (?) compared to the others (?). I heard some people said their laptop runs hotter on DX9 (not confirmed). DX7 DO NOT SUPPORT DISCORD OVERLAY
TL;DR if DX9 works on your PC, make sure to use it. It has huge fps boost compared to any other version.
