Better, stronger, faster, whatever. This is probably more of an odds and mathematics question.

Which is the better deal for the die roller -- adding a Boost Die to a check, or flipping an Ability Die to a Proficiency Die? And is the difference all that great between the two?

I know when to use one or the other, I'm just asking in general which one is the more beneficial.

I think the odds are slightly higher to get more successes/advantages if you add a boost as opposed to just upgrading a single die. But if you're trying to aim for a Triumph for whatever reason, obviously upgrading is the way to go.

Adding a Boost die gives a slightly higher chance for Success/Advantage, and a higher "max possible" Success/Advantage count. But Proficiency dice add the possibility of the Triumph symbol, which is itself worth several Advantage + Success (and cannot be cancelled). Due to the narrative capacities of the dice results, neither is really "more beneficial" than the other, but I would look at as "do you want a higher max possible Success, or the chance for Triumph?"

Here are a couple blog posts from Jay Little, talking about the concepts and ideas behind the dice system. I recommend them for anyone wanting to know more about the dice!

http://gsa.thegamernation.org/2013/01/16/nerd-numbers-terminal-outcomes/

http://gsa.thegamernation.org/2013/01/19/nerd-numbers-a-follow-up/

http://maxmahem.net/wp/star-wars-edge-of-the-empire-die-probabilities/

Chart that shows variables. Bottom line depends if your upgrade turns a green to yellow or adds a green. Turn a green to yellow and odds say adding a Boost is better. Add a green to a dice pool and that is the better, so it depends on what the upgrade does.

Thank you for those links! Very interesting stuff there.

You're welcome.

http://maxmahem.net/wp/star-wars-edge-of-the-empire-die-probabilities/

Chart that shows variables. Bottom line depends if your upgrade turns a green to yellow or adds a green. Turn a green to yellow and odds say adding a Boost is better. Add a green to a dice pool and that is the better, so it depends on what the upgrade does.

I like this guy's take on the dice design this is what Jay said in his first "terminal outcomes" post, in a comment below the main post:

And finally. I’m not a mathematician. That much should be clear. An understanding of math, probabilities and percentages is certainly helpful, but ultimately instincts, gut feelings, and intuition play as large a part as any other factor. The article is meant to be a look at how this concept influences my design outlook, rather than a study of dice pool probabilities. Because the latter would likely make my head explode — which would make it much harder to keep designing games!

It's a good page for just helping to make an informed decision. It's especially helpful to see if there is a choice between do the second Aim or upgrade to a yellow, the Boost die from Aim is the better way to go for Successes and Advantages, people might not realize that.