@Dominic On my machine I get:

records, mb, seconds
25636, 17.430975914001465, 1.001
62658, 45.49252891540527, 2.002
99339, 73.39055728912354, 3.003
133206, 100.99117183685303, 4.004
172779, 130.03430271148682, 5.005
213781, 156.456298828125, 6.006
257011, 182.23061752319336, 7.007
299590, 206.3144016265869, 8.01
338234, 232.39395809173584, 9.011
378044, 258.3344135284424, 10.012
415893, 286.0402135848999, 11.013
454827, 312.4459638595581, 12.014
492972, 338.4016389846802, 13.015
525924, 373.08435440063477, 14.016
565806, 398.6913871765137, 15.017
604355, 425.10098457336426, 16.018
642319, 448.4728412628174, 17.019
648715, 453.09368801116943, 17.196

Is there something I can compare this to?