Last Alioth results I saw LuaJIT was slower than Java, and certainly not in the C ballpark at all.
http://lua-users.org/lists/lua-l/2009-10/msg01098.html shows LuaJIT beating GCC 4.3.2 on some parts of SciMark, and no more than 3× worse on any part. I'm importing the shootout CVS repository into Git, so hopefully we can make some more definitive comparisons soon.
Those overall results show that LuaJIT doesn't really compete much the JVM running under server mode.
On the contrary, although the JVM is always faster, LuaJIT is within about 15% of it on SOR, and never worse by even a factor of 2.
That post is ancient ... here are newer SciMark results for LuaJIT:
Thank you very much! Looks like LuaJIT's beating GCC on almost everything now, and the JVM on most things. But that's with LuaJIT-specialized code that won't run on Lua, which is a little less exciting.