Using the nether portal has essentially no major issues. Using the twilight forest portal, especially multiple times in a short time, causes massive performance loss. Setting twilight forest to false in the config causes the portal textures to break, and still leaves me with a loading screen-less transition pictured below, with the same performance problems. Any way to disable the twilight forest portal functionality properly and retain the loading screen?

A config to disable the transition has been implemented (see #148) but iirc only after 0.2.3 (so it'll only land in 0.2.4).

Which mods (+versions) are you using?
I can see you're using at least 4 possibly unrelated mods. Does the same performance issue happen with just BP+TF (with TF portals enabled)?

Edit:
After jumping through the portal ~100 times, I'm not seeing any noticable performance difference.

Edit 2:
I'm also not getting any missing textures when disabling the TF portal. So same question applies.

Having also just tested it, looks like the performance issues are definitely a "too many mods" problem, also not getting the texture problem with just BP & TF, not sure what mod could be causing it
But there's the mod list, yeah, a touch too many, looks like ill be using that config when 0.2.4 drops

Could you try to remove as many unrelated mods as possible to the point where only relevant ones are left?
Same for the missing texture issue (except I've split it off into #197, so please post any info about it over there).
As is, that's far too many mods for me to manually install them in order to reproduce the issue.