$ node-benchmark-compare <(
  node benchmark/compare.js --old ./node-upstream --new ./out/Release/node --filter buffer-concat buffers
)
                                                                            confidence improvement accuracy (*)   (**)  (***)
buffers/buffer-concat-fill.js n=800000 extraSize=1                                         -2.84 %       ±2.91% ±3.87% ±5.03%
buffers/buffer-concat-fill.js n=800000 extraSize=1024                                *      3.27 %       ±3.06% ±4.08%  ±5.31%
buffers/buffer-concat-fill.js n=800000 extraSize=256                                       -1.75 %       ±1.94% ±2.59% ±3.37%
buffers/buffer-concat.js n=800000 withTotalLength=0 pieceSize=1 pieces=16          ***      7.32 %       ±1.51% ±2.03% ±2.69%
buffers/buffer-concat.js n=800000 withTotalLength=0 pieceSize=1 pieces=4                    1.71 %       ±3.48% ±4.68% ±6.18%
buffers/buffer-concat.js n=800000 withTotalLength=0 pieceSize=16 pieces=16         ***      6.54 %       ±0.56% ±0.75% ±0.98%
buffers/buffer-concat.js n=800000 withTotalLength=0 pieceSize=16 pieces=4          ***      6.03 %       ±1.11% ±1.48% ±1.95%
buffers/buffer-concat.js n=800000 withTotalLength=0 pieceSize=256 pieces=16                -2.18 %       ±2.93% ±3.90% ±5.08%
buffers/buffer-concat.js n=800000 withTotalLength=0 pieceSize=256 pieces=4         ***     11.32 %       ±3.71% ±4.98% ±6.58%
buffers/buffer-concat.js n=800000 withTotalLength=1 pieceSize=1 pieces=16          ***     -5.06 %       ±0.65% ±0.87% ±1.14%
buffers/buffer-concat.js n=800000 withTotalLength=1 pieceSize=1 pieces=4           ***     -7.62 %       ±1.33% ±1.77%  ±2.31%
buffers/buffer-concat.js n=800000 withTotalLength=1 pieceSize=16 pieces=16         ***     -5.84 %       ±0.70% ±0.93% ±1.22%
buffers/buffer-concat.js n=800000 withTotalLength=1 pieceSize=16 pieces=4          ***     -5.99 %       ±0.94% ±1.26% ±1.64%
buffers/buffer-concat.js n=800000 withTotalLength=1 pieceSize=256 pieces=16        ***     -8.78 %       ±2.66% ±3.55% ±4.64%
buffers/buffer-concat.js n=800000 withTotalLength=1 pieceSize=256 pieces=4         ***     -4.70 %       ±1.67% ±2.22% ±2.90%

Be aware that when doing many comparisons the risk of a false-positive result increases.
In this case, there are 15 comparisons, you can thus expect the following amount of false-positive results:
  0.75 false positives, when considering a   5% risk acceptance (*, **, ***),
  0.15 false positives, when considering a   1% risk acceptance (**, ***),
  0.01 false positives, when considering a 0.1% risk acceptance (***)