Is it even possible to get a lv 11 gem? I mean, I have gotten a lv 10 gem on pretty much all of the hidden levels but a lv 11 gem is just crazy. perhaps on the very last level, if you combine all the gems you have and if you spend your mana wisely?!!
If you have maxed skills the guardian really should not be a problem. I had like 8 lv 7-8 gems and many lv 6 gems + lots of ditches to slow him down farther. I only had 2 cyans but you should have more of them, along with more oranges.
there are actually many weapons that add 100+ str, but unless you are using dual swords, you should stick with the flame katana (esp for bio class: 101 speed and 134 str)
baron hurts himself when he is out of focus. he also casts a debuff on himself that doubles your damage. esori, platinum baton (lv 25) adds 191 str as well. I have almost max physical, ice, lightning, shadow, and poison piercing from the awesome corrupted gear.