All shaders have been optimised, with some offering improved performance and others offering poorer performance but better visuals; the following bugs are known:
Bloop is incompatible with the End
Complementary Shaders – Reimagined looks odd on leaves
Light Shader casts a huge shadow in the overworld at a distance; in the End, shadows are bugged; and in the Nether, it’s very dark (this might be intentional, but it looks like a massive cave)
In Potatoshader, the water’s surface looks odd
The FPS figures for the shaders in my benchmark are as follows (using default settings except for render distance set to 64 and ‘beautiful leaves’ enabled):