factoring 1000 numbers in each case (each product of 4 primes)

prime bits    product bits      fails      time  (s)

    5             20              2       0.003317
    10            40              0       0.021160
    15            60              0       0.060126
    20            80              0       0.470410
    25            100             0       2.434207
    30            120             0       13.377470
    35            140             0       125.091811
    40            160             0       702.139568