The Japanese have done some extensive testing of this subject with various weapons (including the Bamboozler's charged+uncharged combo and even some Burst Bomb combos).
Tables and graphs:
http://wikiwiki.jp/splatoon2ch/?%A5%AE%A5%A2%A5%D1%A5%EF%A1%BC%B8%A1%BE%DA
Translation:
http://pastebin.com/WrtAJza1
(Note that on the tables, each sub ability is valued at 3 points and each main ability is valued at 10 points. Thus, 1 main ability is actually worth slightly more than 3 sub abilities.)
Some notable thresholds for the .52 Gal:
1 sub of Damage Up beats
1 main of Defense Up.
1 main of Damage Up beats
1 main and 3 subs of Defense Up (but
NOT 2 mains of Defense Up).
1 main and 3 subs of Damage Up beats
3 mains of Defense Up.
1 main and 5 subs of Damage up beats
3 mains and 3 subs of Defense Up.
2 mains and 3 subs of Damage Up beats
2 mains and 9 subs of Defense Up (the maximum possible while keeping Ink Resistance or Cold Blooded).
3 mains of Damage Up beats
3 mains and 6 subs of Defense Up.
2 mains and 4 subs of Damage Up beats
any amount of Defense Up.
Also, if you're the sort who likes knowing what the "pros" are using, I can tell you that Yugo (a Japanese .52 Gal main on top-ranked competitive team Omohide) usually uses
1 main and 6 subs of Damage Up, which beats
3 mains and 5 subs of Defense Up.