Here is the comprehensive list since we started (please let me know if I've missed anything). Pretty impressive collective effort to come up with these 31 compositions!
69% Poland ¼ thaler 1657 KM#A94 (tdziemia)
68% France 20 francs 1930s KM#879 (erafjel, Hondo Boguss)
67% France 30 sols 1792 KM#606 (ironhorse)
........Germany / Prussia 1/3 thaler KM#303 (spence)
65% Costa Rica 25 centimos 1924 KM#168 (NumisRob)
........Portugal 50 escudos 1971 KM#601 (triggersmob)
64% Austria 5, 10 schillings KM#2882, 2889 (Hondo Boguss)
........Curacao ½ guilder 1941 KM#44 (Hondo Boguss)
........Curacao 1/10 guilder 1944 KM#43 (january1may)
........Netherlands 5 cents 1859 KM#91 (spence)
........Netherlands 25 cents KM#164 (triggersmob)
63% Germany 5 marks 1958 KM#123.1 (mrwhatisit)
........Poland 2 gulden 1770 KM#186.2 (tdziemia)
62% Flanders 4 stuivers 1540 N#96940 (tdziemia)
60% Straits Settlements 20 cents 1927 KM#30b (Hondo Boguss)
........Sweden 25 öre 1907 KM#775 (triggersmob)
Also noted that the pegione of Milan circa 1400 was at around 66%, and that the Kutch 1/2 kori (Y-13) is at 61%. (Note: for some of the Kutch coins listed at 0.61 in Numista, KM has them at 0.601).
59% Poland 2 zlote KM#C-123 (tdziemia)
58% Austria 20 kreuzer KM#1999 (paralyse)
.......Dutch Republic/Holland, 2 stuivers, KM#48 (spence)
.......Hungary, 20 krajcar, KM#432 (paralyse)
.......Spanish Netherlands/Brabant escalin KM#47 (tdziemia)
57% Nethelands 5 cents KM#52 (BCTokens)
........Liege escalin KM#165 (paralyse)
56% German States/Prussia 1/6 thaler KM#299 (spence)
.......German States/Oldenburg 28 stubuer KM#40(Jever) (paralyse)
54% Poland 4 groszy 1767 KM#185 (tdziemia); KM has this at 55%
51% Poland 4 groschen 1787 KM#208.1 (tdziemia); KM has at 55%
50% Australia florin 1958 KM#60 (triggersmob)
........Canada 25 cents KM#62a, 68a (DBM)
........Egypt 2 quirsh 1944 KM#369 (Hondo Boguss)
........France 10 euros 2011 (NumisRob)
........German States/Bavaria 20 kreuzer KM#549.1(paralyse)
........Great Britain florin KM#817a, crown KM#836 (NumisRob)
........Great Britain halfcrown KM#818.2 (paralyse)
........Great Britain 3p KM#848, 6p & shilling KM#852, 853 (Hondo Boguss)
........India ½ rupee 1945 KM#552 (Hondo Boguss)
........New Zealand ½ Crown 1935 KM#5 (Hondo Boguss)
........Peru 1 sol 1931 KM#218.2 (Hondo Boguss)
........Poland 1 gulden 1664 KM#120 (tdziemia, paralyse)
........Portugal 1000 escudos KM#731, 10 euros 2010 (hfjacinto)
........Russia 10 kopeks KM#Y20a (paralyse)
........South Africa 50 cents KM#62 (Hondo Boguss)
........USSR 10, 15, 20 kopeks KM#Y80-82 (january1may)
Noted by january1may that 55% coins include the 10 cents (KM#104a), 25 cents (KM#105a) and 50 cents (KM#109a) of early 20th century Ceylon, and at 52%. several 1/4 florin coins of the Austrian Empire/Franz Josef, KM# 2214-2217. Also noted that the 1/6 talara coin of the Duchy of Warsaw, KM#C85 under Poland is 53%.
49% German States/Saxony-Albertine 1/12 thaler KM#638 (paralyse)
48% Burgundian Netherlands/Brabant 2 gros N#95425 (tdziemia)
.......France, blanc Charles VI (1385-1389) (erafjel)
45% Poland 6 groschen KM#42 (tdziemia)
44% German States/Hamburg doppelschilling KM#419 (spence)
.......German States/Hamburg 4 schilling (KM#359.1) and 8 schilling KM#367 (paralyse)
42% Mexico 50 centavos KM#448 (ariette)
41% Burgundian Netherlands/Brabant 2 gros N# 104038 (tdziemia)
40% Burgundian Netherlands/Flanders, briquet N#248787 (tdziemia)
.......France, blanc Charles VII N#4633 (erafjel)
.......French Indochina 10 cents KM#14 (erafjel)
.......Sweden I krone KM#814 (paralyse)
.......Sweden 5 kronor KM#839 (triggersmob)
.......U.S.
Eisenhower dollar (jbuck, paralyse, kbbpll)
.......U.S.
Kennedy half (paralyse)
I know from this thread
http://goccf.com/t/457142 that 47% exists (maybe someone has an Ottoman zolota?). Aso noted by january1may that medieval Brabant 2 gros coin N#309707 is 43%.
38% German States/Prussia 2 ½ groschen KM#486 (mrwhatisit)
........Lithuania ½ groat Alexander N#31088, 343561 (DBM, january1may)
........Lithuania ½ groat Sigismund I N#63424, 130413 (january1may, DBM)
........Lithuania ½ groat Sigismund II N#35047, 104468, (tdziemia)
........Sweden 1/24 Riksdaler KM#522 (paralyse)
37% Poland 1 groat KM#163 (tdziemia)
36% Lithuania groat KM#10 (tdziemia)
35% Dominican Republic ½ peso KM#15 (ariette)
........Finland 1 markka KM# 49 (triggersmob)
........U.S. Jefferson
War Nickel (Hondo Boguss, jbuck, paralyse)
34% Lithuanian groat 1566 N#46216 (tdziemia)
33% German States/Baden 3 kreuzer KM#211 (spence)
32% France, Charles VIII dizain N#34529 (erafjel)
31% German States/Prussia 6 groscher KM#A297 (spence)
........German States/Prussia 1/24 thaler KM#296 (paralyse)
........Italy/Papal States-Bologna muraiola KM#146? (january1may)
........Silesia/Schweidnitz ½ groat N#65413 (tdziemia)
30% France denier tournois Louis IX N#42076 (erafjel)
........Mexico 25, 50 centavos, peso KM#443, 449, 457 (Hondo Boguss)
Also noted by @paralyse that some 18th century Venetian coins KM#502, 504, 545, 575 are at 39%.
Tomorrrow morning we go to the 20-29% slice. I'm wondering if we can get another 20 compositions before we hit 0?