Side by side comparison to new 4e math (MM3 and Rules Compendium on)
This is all riffing on Quickleaf's DM cheat sheet or Sly Flourish's sheet.
Skills:
No change from New 4e baseline, the harder checks become 15% harder by 20th (+3 - 19 prime stat max instead of 24 prime stats by 18th level).
Damage:
Average NPC Damage reduced by 3:
Current 4e math baseline: 8+level,
Proposed baseline: 5+level
Earlier edition math is all over but 4.5+hit dice isn't far off as a baseline, 3.x increases for stats and items only and accomplishes most damage increases with Full attacks or more powerful spells.
Minion Damage: no change in proportion, however the baseline is 1.5 lower.
Defenses:
Average AC scaling slowed, start +2 higher (at 20th it is 8 lower)
Current 4e math: 14+level,
Proposed baseline: 16+1/2 level
Earlier edition math is all over, 3.x doesn't scale AC, multiple bonuses account for massive increases.
Average Non-AC Defense scaling slowed, start +1 higher (at 20th it is 9 lower)
Current 4e math = 12+level,
Proposed baseline: 13+1/2 level
Earlier edition math (Saving Throws) is between 1/4 and 1/2 except for the Fighters/Creatures at around 2/3 - but pre-3.x non-physical attacks (magic, etc.) didn't scale, 3.x increases at 1/2 HD for good, and 1/3 level for poor - with attacks scaling with stats.
Hit Points:
Hit Points more than halved then shifting to less than halved, NPCs increase HP at the same rate as PCs, they just get 6/7/9 to start instead of Con.
Low HP
Current 4e math = 21+6/level
Proposed baseline: 6+4/level
Earlier edition math = 4.5/HD or lower (d8 HD); d6 in 3.x (or Con penalties)
Medium HP
Current 4e math = 24+8/level
Proposed baseline: 7+5/level
Earlier edition math = 4.5/HD; d8 in 3.x (Plus moderate Con bonus/level 3.x)
High HP
Current 4e math = 26+10/level
Proposed baseline: 9+6/level
Earlier edition math = 4.5/HD or better; d10 in 3.x (Plus high Con bonus/level 3.x)
Attack Bonuses:
Current 4e math = 5+level
Proposed baseline: 6+1/2 level
Earlier edition math = +1/HD or 3/4 HD(level)
Non-AC
Current 4e = 3+level
Proposed baseline: 3+1/2 level
Earlier edition math had no scaling or Stat based DC scaling.
PC Stats:
1e: Stat cap at start of 18, except Fighters (18/00)
2e: Same although some optional races may have gone up to 19.
3.x/4e: Stat cap at start of 20
PC Hit Points:
Current 4e = Con + Class (4/5/6/7) per level plus level 1 bump (6/7/9/10)
Proposed PC hit points = Con + Class only (4/5/6/7) per level (no level 1 bump)
Pre-4e = Class HD per level + Con bonus/level (Max at 1st in 3.x and common house rule before that)
PC Armor Class
Current 4e = 10 + Armor + 1/2 level + bonuses + baked in MW bonus
Proposed = 10 + Armor + 1/2 level + bonuses, no MW bump
Pre-4e = 10 or 0 + Armor + Dex + numerous item/magic bonuses (no set scaling)