Was working on aging a magus by spreadsheet today. A couple of observations about texts.
Upon closer reading, text levels incorporate up to +3 in bonuses for resonate materials and the like. This means a character with Com +1, Good Teacher (+3 texts) and +1 resonate bonus, writes a text at level 11 (sound tractus level).
Primer level texts Level 5, Quality 15 are easy to get, falling into the vain text level (about the same quality is some modern children's books). More desirable are quality 15 tracti (score 14 +1 resonate bonus). Both allow a Magus to go from a score of 0 to 5 in one season.
Intro texts are likely to be level 10 or 11 and quality 20. This will take the reader from 5 to 10 in two seasons.
For advanced texts the magic number is Quality 13. Quality 13 takes a reader for 10 to 15 in five seasons. Anything lower takes six seasons. For arts with an agreed upon standard text, it is probably around Level 18:Q13 or L17:Q14. At L17:Q14 the summa is better XP wise than almost all tracti.
The best regarded book in the order likely either L20:Q14 or L17:Q17. L20:Q14 saves three seasons over going from 17 to 20 using Q11 tracti (12 seasons as opposed to 15 to go from Art 10 to Art 20). It also saves having to hunt down tracti.
L17:Q17 saves one season over a quality 13 text in getting to art score 15 and another in getting to art score 17.
If you are using the large library rules, all of this gets much more complicated.
The upshot is that a great tome is helpful but not really overpowering so.
Studying from Vis is really not worth it except in an aura over strength 5. Powerful specialists may well find it worthwild to live in Regios at the edges of civilization. On the other hand, a Str 10 aura is going to average 16xp per run. Say hi to dragon that likely lives there.