You didn’t say on which machine you did your measurements… Here’s Gambit on a 5 year old intel based machine achieving 0.148 seconds:

$ ./configure --enable-single-host --enable-march=native CC=gcc-9 ; make -j8 ; sudo make install
...
$ gsc -exe fib.scm
$ ./fib
(time (fib 39))
    0.147854 secs real time
    0.147816 secs cpu time (0.147732 user, 0.000084 system)
    no collections
    64 bytes allocated
    3 minor faults
    no major faults
63245986
$ sysctl -n machdep.cpu.brand_string
Intel(R) Core(TM) i7-8700B CPU @ 3.20GHz
$ cat fib.scm
(declare
  (standard-bindings)
  (fixnum)
  (not safe)
  (block)
  (not interrupts-enabled)
  (inlining-limit 1000)
)

(define (fib n)
  (if (< n 2)
      n
      (+ (fib (- n 1))
         (fib (- n 2)))))

(println (time (fib 39)))