Don't think there's a guide to that stuff yet. Most 2nd level weapons cap at level 61, so what you can do is level the weapon up once, and look at the exp difference. If the current level needs 800 exp and the next needs 850, then each level will require 50 more exp. 900, 950, 1000, etc. So you can use that to calculate it. Someone needs to make a calculator for that stuff.
Also, I know that because of the strat book. --- A Blue Slime Appears!
Do you mean the boss or the Tyrant inside the tower? Or the Mark after the boss?
If it's the Tyrant or Mark, you're not supposed to be able to beat them now, unless you super grind. --- Impossible. You can't get killed 9.5 times out of 10. You mean 11 times out of 20. Or you mean 95% of the time. But not 9.5/10. - NInjaZiru