Let me say first off that although I was thinking of a different approach, I don't see any massive problems with the original idea by dindenver. There will always be differing opinions on exactly how to compare the effectiveness of things and I'm sure in time he'd want to tweak a few values here and there but I understand the desire to have an "at a glance" effectiveness rating.
As far as the idea I was thinking of, I'm still working on how to do the math right. So far what I'm looking at is subtracting the defensive skill from the offensive skill. Then (and this is the part I don't have mathed out yet) using something like the 4dF chart on this webpage
http://members.dsl-only.net/~bing/frp/fudge/dice.html to map out a damage curve. Basically work out a chart of what damage would be done without adding weapon ratings on all die roll results and multiplying that by the percentage chance of rolling that result. I had some numbers done up but realized they were skewed as I was writing this: they didn't take into account the additional damage from rolling higher than you need to. Here's the basic equation I would use anyway.
S = static damage per round from skill alone
C = chance to hit
W = weapon rating (if any)
D = average damage per round
S + (C * W) = D
You'd get both C and S from the comparison of the offensive and defensive skills. So far I have C figured but not S, I neglected to figure in the additional damage from rolling higher than you need to. The eventual chart from this will only have about 9 columns and generally speaking you'll only want to see the middle 5 or so. Rolling a -3 or -4 on the dice has a combined likelihood of about 6%. So for any of you that have played D&D, that's roughly similar to telling someone they need to roll a 20 to hit (if defensive skill is 3 or more above the offensive skill) or a 1 to miss (if offensive skill is 3 or more above the defensive skill). Oh, quick note: If you're not using a weapon the equation pretty much simplifies to S = D.
This is only the start of course. Next you have to do another equation but this one I think you can just eyeball rather than get into the math much.
A = armor value
L = length of the stress track
D = average damage per round from equation above
E = number of exchanges it would likely take for the offense to force consequences upon the defense
L / (D - A) = E
Basically you subtract the armor from your average damage you got from the last equation. Divide the length of the stress track by that and you have a rough idea of how many exchanges the offense would need to tag the defense.
Things this wouldn't take into account:
- Fate Points: If you think they'd be in use a lot just factor them into the offensive or defensive skill (wherever you think you'd see them).
- Aspects: Same as fate points above.
- Catches: I don't think there's any possible way to math out a Catch. As a GM you have to just know if your group will work around it or not. If there's a chance it could go either way then be prepared to deal with either possibility.
-Range: I'm just assuming everyone is smart enough to shoot a gun at someone they can't (or don't want to) close with. If they're a speed demon jumping in and out of range, wait and act when they get near.
All of these depend on the playstyle of your group (such as fate point usage and catches) or have common sense solutions (such as range issues).
