Larian Studios Forums Divinity - Original Sin Divinity - Original Sin - General Rebalanced Glass Cannon

Well if you break it down by the numbers:

AP per turn Base
Speed/AP Total = 7/7, 9/8, 11/9, 13/10

Glass Cannon 50% (assuming rounding down)
Speed/AP Total = 7/10, 9/12, 11/13, 13/15

Glass Cannon 100%
Speed/AP Total = 7/14, 9/16, 11/18, 13/20

Effective Speed given by Glass Cannon
Speed 50%/100%
7 = +6/+14
9 = +8/+16
11 = +8/+18
13 = +10/+20

The other thing to consider is that there is an additional way to mitigate Glass Cannon with 1 Talent and Man-at-Arms. So for the price of 2 Talents (Glass Cannon and Picture of Health) and between 3-15 Skill Points you lose between 40-25% Vitality and gain +6 Speed. I'm pretty sure that even the most unlucky of player would find at least 4 points to put in Speed or supplement with equipment by the mid-late game allowing you to spread your points on your primary stat and Con as needed.

At 50% it is like having a free haste every round, this seems at least within the realm of fair. -1 BB/WP would definitely make it a trade-off talent which is what it seems intended to be.