The intensities are still 2-50, for purposes of being rolled, but there is a modifier based on the speed of the weapon, for Mana Leech & Life Leech - this actually uses the SSI property as a factor as well.
Before, it was (stated percentage) chance (the intensity in the 2-50 range, which was effectivey (4% to 100%)/2) that you would get x% mana or life (one is 30% the other 40%) from the damage you did to the target on a hit. Stamina Leech still works that way (at 100% of the damage given to you as that much stamina).
Now, for mana and life leech, it's stated percentage = (property value rolled) * a modifier based on your modified swing speed (speed after including SSI, but not stamina). Instead of triggering x% of the time, it is now triggering EVERY swing, but you get 1-100% * stated percentage * (leech multiplier - either 30% or 40%) * damage from every hit.
Calling it "Leeching" is a bit of a misnomer, as it doesn't actually take points from your target (the way the spells mana drain or mana vampire do), but replenishes your HP/mana/stamina based on the damage done, either way.
using a minor artifact that actually had its leeches go DOWN as an example... (soul seeker)
Old way:
40% mana leech meant that 40% of the time, you would get 40% of the damage you inflicted back into your mana pool (up to your current maximum mana)
Current way: (Base Weapon Speed in seconds * 2500) / (100+SSI property)
On the soul seeker, this results in a displayed 30% value.
Each swing results in 01-30% * 40% * damage returned to the user as mana.
Old Way: averages 16% of damage returned - but could go many times in a row without triggering.
New Way: results in 6% of damage returned each swing (as low as 1%, as high as 12%), but WILL give something back each hit.
The new way is seen by many as a nerf, but actually increases character survivability, as it gives life every hit (to give time for other healing methods to work) and mana (to allow killing of the creature with spells, specials, etc.) to occur more quickly.
The old way, At 120 HP, if you get hit 50 HP a pop - if in the span of those 3 attacks you don't finish a bandage, and if Hit life leech doesn't trigger, you're dead.
With the "nerfed" leeches, you have a chance to have leeched enough to survive the 3rd hit, and enough mana to possibly trigger a special move (even at doubled cost)that will kill it before the 3rd swing.
Personally, I know MY survival rate has gone up, since the changes, with a character whose skills were locked before the changes.