Does postgresql pl/lua language have luajit performance?
According to Luis Carvalho, one of the developers of PL/Lua, PL/Lua can use LuaJIT.

However, you may find there are many more factors which affect the overall performance of the PL code you write, including the overhead of the language's bindings in PostgreSQL, data type conversions, familiarity of your developers with Lua vs. other languages and their ability to write performant code, and many more. There's some more discussion about performance of the PLs you may find interesting.

PL/Lua did do well in a benchmark done by Pavel Stehule.