A little CDF table of block expectation:
0.39346934028737 50.000% 1 in 1.6
0.63212055882856 100.000% 1 in 2.7
0.77686983985157 150.000% 1 in 4.5
0.86466471676339 200.000% 1 in 7.4
0.95021293163214 300.000% 1 in 20.1
0.98168436111127 400.000% 1 in 54.6
0.99326205300091 500.000% 1 in 148.4
0.99752124782333 600.000% 1 in 403.4
0.99872735771441 666.666% 1 in 785.8
0.99908811803445 700.000% 1 in 1096.6
0.99966453737210 800.000% 1 in 2981.0
0.99987659019591 900.000% 1 in 8103.1