What's the highest skill level one can increase up to before potentially wasting skill points?

Assuming one has Comprehension perk and with regard to bobbleheads, what's the highest skill level one can have before start wasting skill points?

As in let's say my char has 99 level repairing skill, then I find two books that increase the character's repairing skill by 1 point, 2 if s/he has comprehension perk, then when the books are read, since the skill level can't go higher than 100, skill points spent beforehand gets wasted as s/he could've gotten to 100 from 96-98 skill points with two books read anyway.

What's the lowest skill level one needs to have by leveling before other skill level increments?

Solution 1:

In order to maximise a skill, you only need to reach lv. 40.

There are 25 books for each skill.

Lv. + Bobblehead + (Skillbooks * Comprehension perk) = Max lv.

40 + 10 + (25 * 2) = 100

Keep in mind that the game still count lv. above 100, just in case a skill is lowered. For example, if you have a lv 102 skill (that the game still count as 100) and you lower that skill by 4, you will reach lv. 98.