Man, I finally did it. What an utterly savage game. The final haul up to Castle Cormanthor took a long time, but it was certainly worth it - with a whole swag of long nasty battles.
I had some trouble with graphical slow downs related to spell effects towards the end (incendiary cloud/cloudkill) and would have to avoid using those spells. It also meant that the final fight with Pelendraalar was particularly irksome due to his breathing ability and penchant to cast incendiary clouds at my mages, who were often hovering about waiting for the right moment to sneak in and heal/apply salves to the fighters. It was a slow and agonising fight and I cursed many times as my fighters flailed away, but eventually the beast fell and to much celebration.
Because it's a dracolich - it brought back memories of encountering Crimdrac for the first time (from Curse of the Azure Bonds).
For the posterity of the thread, here's the details of how my party ended up.
I had some fun with the multi-classing options when my characters all reached the maximum level in their chosen primary classes of 16.
Vastlaar: Level 16 Fighter/Level 3 Barbarian. 187 HP, AC 30, using a trusty Battleaxe+5. He was slow to develop, but ended up being a heavy hitter towards the end.
Thorn: Level 16 Barbarian/Level 3 Rogue. 207 HP, AC 19, using Helm Cleaver.
He was our heavy slugger from the start towards the middle game, then faded a little.
Vigamortis: Level 16 Sorcerer/Level 2 Cleric. HP 49 (there's that low con for you!) and AC 15. His tendency to die must have irritated the hell out of my cleric.
He loved Roderick's Walking stick.
Cassandra: Level 16 Cleric/Level 2 Fighter. HP 94. AC 25. She was much relied upon in the heat of the bigger battles.
Emmeric: Trusty ol' Emm ended up a level 16 Fighter/level 3 Ranger. 178 HP, AC 30. He used Artoth's Bane, which did some monstrous damage towards the end.
Jarial: Level 16 Sorcerer/Level 2 Cleric. AC 25, 101 HP (!). With Vigga, he was integral to winning the game, helping to keep the fighters standing.
Overall, I'm very happy with finally beating this game and can honestly say that it has temporarily sated my love of the classic dungeon crawl.