2010 run = 2000 steps (a 100,000 digits)
2012 run = 4770 steps (a 100,000 digits)
2013 run = 11000 steps (a 100,000 digits)

2013 matches to 2010 until step 1016
2013 matches to 2012 until step 4770

2010-run slowdown factor : 197.5 sec / step
                           0.001975 sec / digit

2012-run slowdown factor : 8.2166666666667 sec / step
                           8.2166666666667E-5 sec / digit

2013-run slowdown factor : 3.1125 sec / step
                           3.1125E-5 sec / digit

immort_estimate_finishtime(2013, 1017)	= 2013-07-22 07:07:42
immort_estimate_finishtime(2013, 1900)	= 2013-09-06 16:58:06
immort_estimate_finishtime(2013, 2000)	= 2013-09-13 17:36:20
immort_estimate_finishtime(2013, 4770)	= 2014-08-17 13:31:31
immort_estimate_finishtime(2013, 5000)	= 2014-09-27 01:01:38
immort_estimate_finishtime(2013, 10000)	= 2018-06-09 01:03:50
immort_estimate_finishtime(2013, 20000)	= 2033-03-25 19:53:12
immort_estimate_finishtime(2013, 30000)	= 2057-11-21 02:02:35
immort_estimate_finishtime(2013, 40000)	= 2092-05-29 19:31:57
immort_estimate_finishtime(2013, 50000)	= 2136-10-17 22:21:20
immort_estimate_finishtime(2013, 60000)	= 2191-01-16 10:30:42
immort_estimate_finishtime(2013, 70000)	= 2255-02-26 10:00:05
immort_estimate_finishtime(2013, 80000)	= 2329-02-16 19:49:27
immort_estimate_finishtime(2013, 90000)	= 2412-12-18 15:58:50
immort_estimate_finishtime(2013, 100000)	= 2506-08-31 23:28:12