With the shift from a D8 to an 8, it changes the probabilities a bit. Instead of d8vd6, it's d12 v. 6
Viz: d8 v. d6
1 2 3 4 5 6
1 1 0 0 0 0 0
2 1 1 0 0 0 0
3 1 1 1 0 0 0
4 1 1 1 1 0 0
5 1 1 1 1 1 0
6 1 1 1 1 1 1
7 1 1 1 1 1 1
8 1 1 1 1 1 1
...where 33/48 hit (69%).
d8 vs. d8 is a 56% hit rate
69/56=1.22x
d12v 1...9
1 2 3 4 5 6 7 8 9
1 1 0 0 0 0 0 0 0 0
2 1 1 0 0 0 0 0 0 0
3 1 1 1 0 0 0 0 0 0
4 1 1 1 1 0 0 0 0 0
5 1 1 1 1 1 0 0 0 0
6 1 1 1 1 1 1 0 0 0
7 1 1 1 1 1 1 1 0 0
8 1 1 1 1 1 1 1 1 0
9 1 1 1 1 1 1 1 1 1
10 1 1 1 1 1 1 1 1 1
11 1 1 1 1 1 1 1 1 1
12 1 1 1 1 1 1 1 1 1
SUM 12 11 10 9 8 7 6 5 4
% Hit 100% 92% 83% 75% 67% 58% 50% 42% 33%
d12 v 6 is 58%, and d12 v 8 is 42% so 58/42 = 1.40x
Shift from 6-->8 a bigger deal than d6-->d8.
Conclusion: Avoid all characters with a d6 dodge.
Happily, 6-->7 is the same as 7-->8, which makes balancing easier.