In my game, the Superior Thunderbolt potion is bugged so that it always increases your critical-hit-chance by 100%, regardless of the weather. I've having quite a bit of fun with this. Just pop a Thunderbolt and use Whirl and watch the heads fly!! And yes --they do literally fly.
On another note, I am currently experimenting with hyrbid builds. My current theory is that due to the law of diminishing returns there is never a reason to have more than 6 skills equipped from any tree. The reason why is that it's possible to have +100% Sign Intensity and +100% Sword Damage by going just 3 into each tree. Therefore, the only reason to go further than that is for the tactical advantages skills bring. I think this theory synergizes especially well with the Sign tree because it's well suited to switching out skills to adapt to the situation.
Here are some theoretical builds that go along with this theory. NOTE: the skill calculator isn't working properly, but I'm sure you can guess what the last 3 skills are.
Swordsmanship Focused Hyrbrid and
Signs Focused Hyrbid. Both these builds have the following bonuses.
One Greater Red Mutagen = 40%
Superior Oils = 50%
Muscle Memory = 25%
Superior Thunderbolt = 35%
Total Fast Attack Damage = 150%
One Greater Blue Mutagen = 40%
One Greater Blue Mutagen Unlinked = 10% (in slot next to General Skills)
Superior Phitri's Philter = 20%
Base Sign Intensity = Geralt's Level +1 (I will assume level 30 for this example)
Total Sign Intensity = 101%
Additionally, you can swap out Feline Armor for Griphin armor if you want. Whichever one you go with will add 45% Fast Attack damage or 45% Sign Intensity. You can also swap out Rage Management for Focus or Adrenaline Burst, but I
vastly prefer Rage Management. If you're lacking Adrenaline Points just equip +Adrenaline Glyphs in your swords. Whichever build you decide to go with, you will get either +40% Sword Damage or +40% Sign Intensity from the Greater Mutagen linked to your last 3 skills.