25% +7 to +9 scroll distribution

1) Has anybody used these and/or know what the distribution is on the m/atk boost? Equal for all 3? Approximately normal distribution around 8? (~Exponential decay) Highest at 7 and lowest at 9?

[Doesn't make sense to make a separate thread for this:]
2) Should I try using these on my weapon instead of Red 50% +8s? I currently have 190 MATK on my empress staff with 7 slots left; scrolling the rest with +8s (if I even succeed) will get me to 246 MATK, 4 shy of 250 (which is best for enhancement AFAIK?). I have fairly limited resources, so I don't think I can afford 90% +9s, and I won't be scrolling another weapon for a very long time.

1) Based on my own + others' past experience, a skewed distribution toward the right (7 being left, 8 being middle, 9 being right) had been observed, meaning that landing +7-8 had occurred more frequently than landing a +9. There's no definitive means, however, to substantiate the idea that this observation matches the actual scroll distribution.

2) Is gaining a few more M.ATT worth the cost of spending extra nx on protection scrolls, guardian scrolls (if you don't have an ample supply of the booming 25%'s), and/or return scrolls (in the event you land a +7)? From a cost-to-benefit analysis, I would say it's wiser to go with the RED 50% +8 att scrolls.

Seeing how the RED scrolls are 50% and no boom, unless you are ready to burn through a lot of money I would recommend using the RED scrolls. You mention limited resources, and you should know your limits. If you have limited resources then you probably are not going to make a 10+ star weapon where the 4 matt would make a difference. The chances of getting 4 9's is pretty slim anyways, so don't bother.

1) Based on my own + others' past experience, a skewed distribution toward the right (7 being left, 8 being middle, 9 being right) had been observed, meaning that landing +7-8 had occurred more frequently than landing a +9. There's no definitive means, however, to substantiate the idea that this observation matches the actual scroll distribution.

This has been my experience with these scrolls as well.

Seeing how the RED scrolls are 50% and no boom, unless you are ready to burn through a lot of money I would recommend using the RED scrolls. You mention limited resources, and you should know your limits. If you have limited resources then you probably are not going to make a 10+ star weapon where the 4 matt would make a difference. The chances of getting 4 9's is pretty slim anyways, so don't bother.

I suppose I should have said I have limited liquid assets/buying power, as I do have a fairly large stockpile of prots, slates, AEEs, and some return scrolls. But given that +9s are rarer than +7/+8, going with RED scrolls does make more sense. Thanks to everyone who replied!