About speed reduction: I think the game should be
fun. Imagine your party walking around in Atkathla allways having to wait for
Mr. Keldorn to catch up ... You'd need way more micromanagement while you are in a dungeon. Do you want your light weight mage to arrive first at the enemy? Didn't think so. So you'd have to split up the party for your now awfully slow tanks to be the first to get hit. Not really funny if you ask me.
I play
IWD 1 at the moment with a system like
T.G.Maestro's The Dex penalty is oriented around the
weight of the armor. The heaviest (Full Plate, 70 lbs) gives a penalty of 7. Armor between 51 and 60 gives -6 and so on down to 1-10 giving -1. Since magical armor usually weighs less than normal armor this reflects the enchantments too - at least a bit.
Shields lead to even more penalties (Bucklers, Small: -1, Medium: -2, Large: -3). Here I didn't take weight into account but maybe it could be done here too.
Resistance: I think your numbers are way too high. A cleric wearing a full plate (70 %) and casting armor of faith (max. 25 %) is
nearly invulnerable (95 % resitance to all). I have split it up as follows:
Leather: no enchantment to +5 gives 7 to 12 %.
Chain/Splint: n/e to +5 gives 9 to 19 %.
Plate/Full plate: n/e to +5 gives 14 to 24 %.
Then I looked at the special
AC bonuses (f.ex. plate mail: -3 vs. slashing) of each armor, applied that number as an additional percentage (normal plate mail now gets 17 % vs. slashing). With shields I did the same thing. (Bucklers/Small: 2-10 %, Medium: 4-12% and Large: 6-14 %, special
AC bonus converted into % increase/decrease).
I know, this isn't realistic (f. ex. the DEX penalty doesn't take the character's strength into account) in any way but its quite playable and a bit more believable than the original system. And I actually tend to
keep my magical armor. A chain mail +2 now is a better suit of armor than a normal plate mail. In vanilla
BG2 or
IWD I'd sell the chain mail, buy a normal plate mail (same
AC but waaay cheaper) and a lot more stuff with the remaining gold.
Wolfgang