[bestboy]

One can improve the JAVA result by allowing the JIT compiler to inline the recursive calls.

   -XX:MaxRecursiveInlineLevel=1 (default): 6.667 s
   -XX:MaxRecursiveInlineLevel=2:           6.141 s
   -XX:MaxRecursiveInlineLevel=3:           5.768 s
   -XX:MaxRecursiveInlineLevel=4:           5.400 s
   -XX:MaxRecursiveInlineLevel=5:           5.361 s
   -XX:MaxRecursiveInlineLevel=6:           5.072 s

For comparison

   fib.c with -O3: 3.764 s

edit: formatting and adding more data points