I went that with my first 4mages group but I don't think the shaman adds anything, so my new 4mage setup is runepriest x2, druid, freemage. If spells weren't so expensive, I'd probably drop the freemage but really need that ID and secret detection to save at least that. Druid is great for healing cause you can cast Regeneration+Stoneskin+the "HoT" they get when promoted and basically it does all the healing automatically for multiple turns, then you can spam blizzard or whatever. One runepriest goes Light magic for secondary healing and fire for dmg, other pure fire/magic focus.
4mages actually seems it'll be broken OP once you reach GM on all 4. As in, kill everything in sight in one round, even the mega large packs at the end. It's only rough the first 10ish levels or so, basically act1(and it's not even that rough if you know what you're doing, gust+entangle, or just entangle are your best friends early on imo, I get both on druid and freemage to juggle melee mobs, plus entangle is actually a really good nuke if you level earth on the druid).
As for the question on my optimal party, with just finishing the game in mind(not like killing the cyclops/shadow dragon early or challenge based stuff), I actually think 4mages might be the most optimal, even if it can be shaky early on. In a more traditional party setup, you generally want a freemage in every group for secret detecting, but if you know where the secrets are beforehand(you've played the game already), you could drop him and get a better character.
Assuming you don't though, Freemage(2spirit 2vit for the first 10 levels or so, then 2spirit 1vit 1magic for a while, then 2magic 1vit 1spirit, like say starting 20) with Air/Focus GM, primordial expert, dark expert or master(choice depends on your melee DPS, if you go dagger bladedancer then you want master, if you go barb then you don't). Utility bitch for IDing and secrets detection, also purging shit, then air nuker when not doing that, want to pump vit higher since it's the squishiest character and you don't want to constantly rez him. Consider using the vit and +5health potion on this guy.
Runepriest with GM Earth + Fire and Expert or Master Light(depends on your tastes), 1pt shield(or more later on), 1pt medium, 1magic 1vit 2spirit for the first 15-20levels then 2magic instead. Basically the healer/buffer but can nuke with fire hard when there's no need to heal.
Crusader, GM sword+light, see the guide a few posts before on how to level that one. Support healer, does good damage.
Bladedancer or Barb. The choice here varies, but for example with paladin and master dark on your freemage, you get 2 insane flat damage buffs, so a dagger blade dancer would hit for +60damage flat, per attack. Count 6attacks per round when GM dagger, that's 360damage, not even counting your own damage. That said, that's a late bloomer, dagger GM trainer is the lastest you can reach in the game and is basically right before the end of the game, with only 4attacks it's not quite as good, also no relic daggers I believe. For a more consistent experience, I'd go spear barb. In terms of skills, GM spear+2H for the barb, GM dagger+DW for the bladedancer. Dump spare points in defensive shit. Probably ignore destiny on both of these since they don't get too much out of it(spear and daggers don't have "on crit" effects like sword/axe/mace), and instead do 3might 1vit, with maybe a few levels being 2might 2vit for early safety, but they start with high health so not sure it's needed. Might want to dump +5mana pots and +1spirit pots on your bladedancer so he has mana to use his aoe, but shit's so expensive you probably won't get much use out of it.
