Also shields can block elemental bolts, LCSs, Iron Shots and OODs and I find that makes them effective against a great majority of the mid and end-game threats. It's when you hit torment and Hellfire that they start tearfully waving goodbye, but I've generally felt safer on Shields dudes even then. Fiends may torment you 3 times in a row, but they're just as likely to Bolt of Ice you three times in a row, and those can hurt like hell too.
Shields can not block elemental bolts. If they could, maybe more people would consider using them, as elemental bolts are a pretty common source of high damage throughout the game.
Can anyone point me a formula of how armor penalty is calculated? I'm going to use Ring Mail (because if resistances) as a DECj. I have Str 5 and get my Armor to 5 to lesse the penalty. It is easily manageable since my hardest spell is battlesphere, but I want to have nice EV later on and excellent spell success of my Firestorm or LCS.
I understand that i may find a good robe to replace my ring mail and all the work wil be just a wasted xp and stats. But if that ring mail can be managed with little effort (such as 6-7 str and 10 Armor), I will be glad to get it soon. This will widen my choise from robe-leather to robe-leather-ringmail.
Str 5 is a bit low, even for ring mail, but the penalties aren't going to be too severe either way. Basically, if you can still cast your spells in it, don't worry about it.
Training armor skill is a good way to raise the AC you get from armor. It's not an efficient way to increase your EV or spell success chances, instead you should just train the relevant skills. However, even a character in light armor benefits from armor skill, so it's not a waste, although probably not the most efficient use of your XP.
Also, is 5 in shield are enought to nullify the buckler spellcasting penalty?
I would be glad if someone can share links to trunk source code where I can look at all the calculation.
I'm pretty sure 1 skill in shield is enough to nullify the buckler spellcasting penalty, while 5 skill will nullify the melee penalty. A buckler is a really good defensive addition to a spellcasting character, since it takes very little investment.