The validation time also grows exponentially with the number of items:

0 items, avg. validation time: 0.078653 ms
1 items, avg. validation time: 0.233635 ms
2 items, avg. validation time: 0.277518 ms
5 items, avg. validation time: 0.442096 ms
10 items, avg. validation time: 0.386543 ms
20 items, avg. validation time: 0.352659 ms
50 items, avg. validation time: 0.69204 ms
100 items, avg. validation time: 1.090923 ms
200 items, avg. validation time: 2.762619 ms
500 items, avg. validation time: 7.474321 ms
1000 items, avg. validation time: 27.675976 ms
2500 items, avg. validation time: 184.583688 ms
5000 items, avg. validation time: 624.382551 ms
7500 items, avg. validation time: 1262.320178 ms
10000 items, avg. validation time: 2125.455512 ms
20000 items, avg. validation time: 8322.531352 ms
30000 items, avg. validation time: 19281.462 ms