Hi Mike, how are you?
I've not run the Battle of Iceland, since my campaign is still in 1620 (end of) and my players are dealing with Than Ulbar at the moment. They have already won the field battle, breached the walls, forced their way through the guts of the High Temple of Thanatar and killed Chsa Glut, so I think they are almost finished with that scenario.
BUT, as a narrator experienced in managing powerful characters myself, let me advise you, who I greatly appreciate as an author, since The Tower of Ivory HQ and Strangers in Prax and Shadows on the Borderlands, about dealing with mighty heroes.
Yours seem quite strong in melee combat, but vulnerable at missile range. Also well aimed magic, numbers, discipline and organization (on the foes' side) can keep at bay even the most powerful of heroes.
i.e. In my campaign (which started in 1989), the heroes are in the 4 mastery range and able to defeat a sixmastery single guy, like Chsa Glut, after some calculations are made and losses are accepted. I know that they are able to, because they DID so and I didn't fudge (nor can they, since, alas, we play online).
Finally, even if heroes are powerful, they must have weaknesses, and, just to simulate the fact that opponents might know and purposefully strike at their soft/weak spot, you should make any effort to lure them in a trap or make them fight one another or simply trick and bluff them away.
Ciao,
Gian
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