Count me in as team CSiT. Sea of Madness is a great song (doesn't quite hold a candle to Caught Somewhere in Time though) - but there's quite a few soaring vocal parts that would be just as hard (if not harder) than the high vocal parts in CSiT.
Also, Bruce gets less time to rest between verses/choruses in Sea of Madness. Not to mention that only the choruses of CSiT are really difficult to pull off (vocally) and Bruce mostly repeats the same melody several times in a row (Aces High has more variation within the high vocal range than CSiT, for example).
As for Nicko, there's some pretty sick fills in SoM, but I'd agree with the majority of the forumers here that CSiT is more difficult from a drumming perspective. I don't believe that CSiT is considerably more difficult from a vocal perspective than SoM is however.
And vocals and/or drumming experts that could affirm or deny my theories? I think there's a greater than 90% chance that we will hear the epic, crushing, and brutally melodic CSiT live on the next tour. And I'm happier than words can describe.