For those who haven't already come across this, this site allows you to calculate your chances of obtaining skill vs success rate based upon entering your skill values vs the skill cap, as well as the crystal you're using and the current day (and calendar days in the future).
Enter the values, and find a result value on the table to the right between 2-4 (if possible) if there are no good values, pick a different day on the calendar.
http://ffxi.lokyst.net/timer/crafttimer.html
This below explains which values are best for what.
Quote:
<0 The Redundant zone
- Skill ups can be harder to attain
- The recipe is too easy to improve your skill
- Just too many factors helping you succeed, so no chance to learn
0-2 The Success zone
- Very good rate of success
- Skill ups will happen, but some will be lost due to the recipe being easy to your current skills.
- Best used when the recipe is break even or profit, and/or when the ingredients are expensive.
2-4 The Prime Skill up zone (Aim for this)
- Very good rate for skill ups
- Failures will happen, but at a fair trade off for skill ups (in most cases)
- For anywhere from 7/8-1 levels from cap, it is fairly easy to get the "X" to be in this range
4-6 Skill from fails zone
- OK rate for skill ups
- Best to be within 5 levels of cap so that skill ups can still be gotten from failures. 5 is not the "X" value, but just the rigid calculation of cap - skill.
- Supplies better be cheap, or you will be digging yourself into a hole
>6 High risk, low reward zone
- No good reason to be in this zone
- Only for the pure power leveler, who could care less about expenses
- Please move onto another craft/recipe before wasting your gil here.