Target Numbers versus Challenge Levels

While looking out at the clouds today, this thought came up:

"Dice + Modifier >= Target Number"

or

"Dice + Modifier - Difficulty >= Fixed Number"

SBRPG chooses the latter method for two reasons. One, difficulty is directly rated on level, which is equivalent to character level. A level 5 thief picking a level 5 lock has a base 50% chance of success (without ability modifiers). Ability scores bend the curve, allowing you to do better with better scores. The second reason is successes depend on the amount the roll beats the fixed target number. It is easier to do some math during the roll to keep the number range down, so calculation of the degree of success is easier.

The first method sets a target number, such as 25, and lets players add up modifiers and their roll to reach it. It is a simpler system, in that it does not require the subtraction step, but it is a bit more obscure in that the target number does not mean much. Of course, TN = Level + 10 in SBRPG-terms, but the mechanic seems more prone to made-up target numbers than real level-based difficulties. The system is also prone to blow-out at the high end, since there is less of an urge to cap the target number. Finally, calculating successes requires more math, for example:

The dice roll is 12
The modifier is 7
The problem level is 5
The fixed number is 11+

12 + 7 >= 16, true; a total of 19 - 15 = 4 successes

or

12 + 7 - 5 >= 11, true; a total of 14 - 10 = 4 successes

In the 11+ fixed number, you take 10 off the difference to determine successes. The second method of "knocking 10 off the roll" to determine the level of success is easier math than (roll minus 10+PL). Why is the success number so important?

Success measures the level of the job performed. In the above example, let's assume this was the level 5 thief picking the lock. The job was done at a level 4 of a result, at or near the thief's level of 5. We can assume this was an average job result for a level 5 thief. Let's say the thief only rolled one success, that would be more like how a level 1 thief would have picked that lock - it would have been a messy job, taken a while longer, made a lot of noise, and so on. If the thief rolled high, say an 18, and got 10 successes, that would tell you the thief did that job as efficient, fast, and quiet as a level 10 thief's average lockpicking attempt- smooth, quick, and quiet.

SBRPG has a whole "skill level versus problem level" mechanic, and using successes as "result level" gives the dice rolling system a nice tight, immediate, and X vs Y = Z feel.