I once played a very lucky dual-class ranger/magic-user with a high Constitution. For this character, I was fortunate to roll maximum or one less than maximum with every hit die I rolled. A 10th level mage with 84 hit points seriously kicks ass!
As Judge, I’m glad I’ve never seen a player be unlucky enough to do the opposite, roll 1 or 2 on every hit die rolled. One assumes a fighter with such poor luck would not survive for long, irrespective of Constitution.
I’ve made several ACKS custom classes, and I am struck by how relatively expensive hit die are. (This is not a problem with the construction system, but simply a reflection of the original game.) As a Judge, I like to throw the kitchen sink at my players, but without the speed bump to play of TPKs. I also like “organic” characters created with an element of randomization.
With all of the above in mind, I am currently trying out the following rule (for PCs and selected NPCs) to reward a class’s investment in hit die.
Maximum hit points at 1st level.
Classes with Hit Die 0 and Fighting 0 roll 1d4 per level.
Classes with Hit Die 0 and Fighting 1+ roll 2d4 per level, taking the highest die.
Classes with Hit Die 1 roll 3d6 per level, taking the highest die.
Classes with Hit Die 2 roll 4d8 per level, taking the highest die.
Also, an element from 1st edition that I liked.
Classes rolling a d4 hit die gain 11d4 through 11th level before adding their class constant value.
Classes rolling a d6 hit die gain 10d6 through 10th level before adding their class constant value.
Classes rolling a d8 hit die gain 9d8 through 9th level before adding their class constant value.
Bottom line using this method, at 11th level on average, a fighter will gain 22 hp over a mage, a cleric will gain 17 hp over a mage and a thief will gain 9 hp over a mage.