Godly Scrolled Items

20% = 3 all, 9 atk
50% = 5 all, 5 atk

20% vs 50% ==> 4 atk vs 2 all stat

==> 4 atk vs 6 total stats

Only a really really really screwed up xenon would make it so the 50% provides more range than the 20%. However the 20% route is much more difficult to complete. In terms of perfection though, 20% is better.

You'd need an extremely high w.atk for that to make sense, yeah.

My Xenon's got 207 att and ~290 in each stat, and it's roughly 2 atk = 3-all:

 Spoiler

(this is comparing 6-all 5 att to 3-all 7 att - you can see my stats are higher than 290, this is the %all bonuses)
More atk is only going to be worse than more +all if you have a higher total atk than your total in any of the stats. (only the base amount, without %stats, but still, it's a fairly high number - as my level 69 xenon has 290 already, on a base of 120 per stat).

For the 50% to be better, you'd need 2x as much w.atk as your base stats - so if you had, say, 800 in each (due to Tempest gear etc.) you'd need 1600 w.atk.