I don't know which code Brendan was using, but using the http://shootout.alioth.debian.org/ implementations I ran some tests of my own:

  Performance counter stats for './nbody.gcc_run 50000000' (5 runs):

       6232.525219 task-clock                #    0.999 CPUs utilized            ( +-  0.09% )
               533 context-switches          #    0.086 K/sec                    ( +-  0.43% )
                 1 CPU-migrations            #    0.000 K/sec                    ( +- 66.67% )
               166 page-faults               #    0.027 K/sec                    ( +-  0.15% )
    27,385,819,080 cycles                    #    4.394 GHz                      ( +-  0.05% ) [83.31%]
    19,494,722,200 stalled-cycles-frontend   #   71.19% frontend cycles idle     ( +-  0.07% ) [83.30%]
     6,403,657,640 stalled-cycles-backend    #   23.38% backend  cycles idle     ( +-  0.21% ) [66.70%]
    31,905,910,193 instructions              #    1.17  insns per cycle
                                             #    0.61  stalled cycles per insn  ( +-  0.01% ) [83.37%]
     1,902,954,908 branches                  #  305.326 M/sec                    ( +-  0.05% ) [83.36%]
            39,925 branch-misses             #    0.00% of all branches          ( +- 31.16% ) [83.34%]

       6.239027874 seconds time elapsed                                          ( +-  0.08% )


  Performance counter stats for './nbody_rustc 50000000' (5 runs):

       6970.131625 task-clock                #    0.999 CPUs utilized            ( +-  0.07% )
               601 context-switches          #    0.086 K/sec                    ( +-  0.33% )
                 5 CPU-migrations            #    0.001 K/sec                    ( +-  7.41% )
             1,024 page-faults               #    0.147 K/sec                    ( +-  0.02% )
    30,587,917,853 cycles                    #    4.388 GHz                      ( +-  0.04% ) [83.31%]
    19,368,464,950 stalled-cycles-frontend   #   63.32% frontend cycles idle     ( +-  0.06% ) [83.34%]
     7,348,766,082 stalled-cycles-backend    #   24.03% backend  cycles idle     ( +-  0.84% ) [66.69%]
    36,479,184,126 instructions              #    1.19  insns per cycle
                                             #    0.53  stalled cycles per insn  ( +-  0.01% ) [83.35%]
     2,404,008,283 branches                  #  344.901 M/sec                    ( +-  0.04% ) [83.35%]
            65,846 branch-misses             #    0.00% of all branches          ( +- 11.89% ) [83.33%]

       6.977211938 seconds time elapsed

The C version is here: http://benchmarksgame.alioth.debian.org/u32/program.php?test... . It appears to be the fastest C verson on the site. The Rust version looks pretty gross (it's likely very old code), I'd like to try porting the C version to Rust (it's only 140 lines) and compare the results. Note also that I'm using a version of the compiler that's so new that it's not even in the official repo yet, containing optimizations for floating-point math.