I am no mathematician but this is relevant to a rp I'm DMing at the moment. We use D6s only though. 3d6 in a stat means it's your best stat, 2d6 means your pretty competent. In this system a 6 is a success, a 4 or 5 is a Mixed Success, a 1 to 3 is a failure and two 6's are a critical success.

Here are the percentage chance of rolling something on a D6 system:
[center][img]https://i.gyazo.com/b48dee7cc11ae0c1d5c91a1a09192b38.png[/img][/center]

I'd be [i]really[/i] curious to see how much % chance switching from a D6 to a D8 actually affects your chances though. Now you've got me looking up the system...