Might as well put this here since it seems relevant to the discussion:
Gunnery
1: +2.5% ranged to hit
2: +5% ranged to hit
3: +7.5% ranged to hit
4: +10% ranged to hit
5: +12.5% ranged to hit, Multi-Target skill
6: +15% ranged to hit
7: +17.5% ranged to hit
8: +20% ranged to hit, Breaching Shot skill
9: +22.5% ranged to hit
10: +25% ranged to hit
Piloting
1: +2.5% melee to hit
2: +5% melee to hit
3: +7.5% melee to hit
4: +10% melee to hit, +1 unsteady threshold
5: +12.5% melee to hit, Sure Footing skill
6: +15% melee to hit, +1 hit defense, +3 melee defense
7: +17.5% melee to hit, +20% Sprint Distance
8: +20% melee to hit, Ace Pilot skill
9: +22.5% melee to hit, +2 unsteady threshold
10: +25% melee to hit, +3 hit defense, +6 melee defense
Guts
1: -5% chance to die when incapacitated
2: -10% chance to die
3: -15% chance to die
4: -20% chance to die, Health 4
5: -25% chance to die, -1 recoil penalty, Bulwark skill
6: -30% chance to die, +15 Overheat Threshold
7: -35% chance to die, Health 5
8: -40% chance to die, -2 recoil penalty, Coolant Vent skill
9: -45% chance to die, 30 Overheat Threshold
10: -50% chance to die, Health 6
(base chance to die is 90% by center torso destruction and 140% by head destruction)
Tactics
4: -1 indirect fire penalty, identify type of contact
5: -45m min range, Sensor Lock skill
6: Called Shot Bonus (2.4 multiplier to base chance)
7: -2 indirect fire penalty, identify tonnage of contact
8: -90m min range, Master Tactician skill
9: Called Shot Mastery (3.75 multiplier to base chance)
10: -3 indirect fire penalty