TheBGAnt: 20 lvl spells are 20 lv spells.
Yes, and level 1 spells are level 1 spells. What is the point of this tautology?
In the case of a Fireball, a clvl 40 caster can deal ~1120 damage with slvl 19 or ~1260 damage with slvl 20. Either one will easily kill fire-susceptible enemies. Neither one can one-hit or two-hit kill a Blood Knight, but both can three-hit kill a Blood Knight. So if you do not need an extra shot to kill the target, what value are you getting from that last slvl?
In the case of Chain Lightning, slvl 19 vs slvl 20 gets you one extra frame of duration for the lightning bolts, which will increase the damage slightly. However, your biggest problem with Chain Lightning will be gaps due to spell effect limits, and the gaps will impact both levels substantially. As I read the description of the spell, the extra slvl will not increase the number of bolts generated, and the per-frame damage is independent of slvl. I doubt one extra frame of damage will make the difference in whether a monster survives to need an additional shot.
TheBGAnt: I don't know if it's ok to have such high lvl spells but for example if with sorc I clear hell/hell for x time then the time to clear it with warrior is something like X +~40% more and with rogue will be X +~60% time and I would not use a bow as it way too dangerous to do that.
Yes, of course non-sorcerers are slower. Using a bow is perfectly feasible though, if you manage monster activations carefully.
TheBGAnt: I use only items which had -LR. I have no idea why in the world you would want to make pointless teleports around the level to have the problems you are referring?
I would never make a pointless teleport, because by definition it would be pointless. I would however make useful teleports if it let me skip over enemies that were not worth my time to kill. If I'm going for maximum time efficiency for experience points, I want to engage only monsters that can be killed quickly with Fireball or Chain Lightning, and run past everything else. For that matter, if I want maximum experience, then I'm probably better off playing in Nightmare/Hell. The +15 mlvl boost in Nightmare is enough to keep monsters worthwhile until I start to approach clvl 40. Even after that, the increased speed of fighting weaker enemies with generally worse resistances might make the reduced experience a worthwhile trade. If I'm going for maximum time efficiency for items, I wouldn't be in Hell/Hell at all, because the drops in lower difficulty games are just as good, and the enemies are easier to kill.
TheBGAnt: My hero levels are Sorc 43, Warrior 42 & Rouge 41 and have no problems to do hell/hell with a Sorc when I have huge huge problems to do that with a Warrior & Rouge.
So we have established that you aren't good at Warriors or makeup. Plenty of people have completed solo runs of Hell/Hell at clvl 30, as part of the 3@30 ritual.
TheBGAnt: To be honest i don't remember to have died more then a single digit on hell/hell with a Sorc when I have no problems to die there with the other 2 heroes if they are not at -80% LR.
Again, this sounds like a playstyle problem. Perhaps you activate too many monsters at once.
TheBGAnt: I have cleared hell/hell with rouge with bow with no -LR but that's the time x 3 vs Sorc time and even more if I have an ugly level with succubus & lava maws. It's pointless obviously to lose so much time.
Pointless, but very possible. To pick an ideal area, you first need an objective. Are you playing for maximum experience per hour? The best items? The greatest challenge?
TheBGAnt: I don't see how -5 spell levels & sword and shield is more effective when I don't have any problems to start with on hell/hell with a Sorc.
There are no items that reduce spell level by 5. I never said to use a sword/shield combination. I said to use a Dreamflange and enchanted shield, because you can get better bonuses that way than with an Arch-Angel's staff, and the practical consequences of the one slvl loss from using a Dreamflange is,
in my opinion, more than offset by the stat bonuses. Although the Dreamflange is considered a Mace, you wield it for its specials, not for use as a melee weapon.
TheBGAnt: The only thing which I see as effective for that build is to use it in when you play with a friend as it is impossible to use non stop fireballs and CL with someone else is with you. Then and only then that is a good choice.
Yes, Chain Lightning is unpredictable, but Fireball is still very possible if you mind where your friends are.