Realistically I think the way to look at it is right now is that with these ranges: (1/8 of the range)
[8000000000000000:9000000000000000],[9000000000000000:a000000000000000],[a000000000000000:b000000000000000],[b000000000000000:c000000000000000],[c000000000000000:d000000000000000],[d000000000000000:e000000000000000],[e000000000000000:f000000000000000],[f000000000000000:ffffffffffffffff]

The most likely spots (first guess) are possibly here: (inner half of the range, 1/16 the range)
[a000000000000000:b000000000000000],[b000000000000000:c000000000000000],[c000000000000000:d000000000000000],[d000000000000000:e000000000000000]

I believe that low range keys are over represented so far:

1:1,1,1/1
2:3,2,1/2
4:7,3,1/3
8:8,4,2/4
1:1,5,3/5
2:3,6,3/6
4:4,7,4/7
8:e,8,4/8
1:1,9,5/9
2:2,10,6/10
4:4,11,7/11
8:a,12,7/12
1:1,13,8/13
2:2,14,9/14
4:6,15,9/15
8:c,16,9/16
1:1,17,10/17
2:3,18,10/18
4:5,19,10/19
8:d,20,10/20
1:1,21,11/21
2:2,22,12/22
4:5,23,12/23
8:d,24,12/24
1:1,25,13/25
2:3,26,13/26
4:6,27,13/27
8:d,28,13/28
1:1,29,14/29
2:3,30,14/30
4:7,31,14/31
8:b,32,14/32
1:1,33,15/33
2:3,34,15/34
4:4,35,16/35
8:9,36,16/36
1:1,37,17/37
2:2,38,18/38
4:4,39,19/39
8:e,40,19/40
1:1,41,20/41
2:2,42,21/42
4:6,43,21/43
8:e,44,21/44
1:1,45,22/45
2:2,46,23/46
4:6,47,23/47
8:a,48,23/48
1:1,49,24/49
2:2,50,25/50
4:7,51,25/51
8:e,52,25/52
1:1,53,26/53
2:2,54,27/54
4:6,55,27/55
8:9,56,27/56
1:1,57,28/57
2:2,58,29/58
4:7,59,29/59
8:f,60,29/60
1:1,61,30/61
2:3,62,30/62
4:7,63,30/63
1:1,65,31/64
2:3,70,31/65
4:4,75,32/66
8:e,80,32/67
1:1,85,33/68
2:2,90,34/69
4:5,95,34/70
8:a,100,34/71
1:1,105,35/72
2:3,110,35/73
4:6,115,35/74

Nearly ~47% of all the keys found were within the first 1/8th of the range.
Having them at the far end (7/8) and the beginning would seem not particularly random.
So if I am right then puzzle 64 is only about 2^59 in range.