good question.
on drums, the song 'worlds' is very hard all the way thru as it's very rigid technique wise.
as is 'the caller and the listener'- the double bass at the end for ages
all the drum parts are hard to play (the same as on the album), i just struggle with some more than others. the bits with fast double bass for ages are the hardest, the hands dont pose too much of a problem.
guitar wise the hardest solos to play technically are:-
solos after last vocals in'worlds beyond the veil'
solo before clean break in 'beyond the eyes of man'
solo at end of 'transcendence'
and in terms of vibe, getting the right feeling: -
solos in 'psyrens'
solos at the start of 'the sands of time' (particularly the 3rd one)
its hard to say one is harder than the other, in truth its challenging to get any of the solos sounding exactly right, i spent ages on them when recording as it was always about capturing a feeling with each one. i reckon i got pretty close with most of them. it's not about the technique per se, its about using the technique to create a feeling.
i reckon one of the best feel wise solos is the ambient mid solo in transcendence, thats a cool one.
the psyrens solo was done by me in one take in 2001, i just blasted it out and doubled it, with a slight difference in the 2nd take (the pick tapped run over the blast diverges).
i wrote the song in one night, and then added solos over the top in a few goes, just kept the ones that sounded good at the time, these have gone on to become THE solos
the reason its hard to replicate is because its one of my only solos where 2 guitars are playing slightly different things. so its not actually possible to play both parts at once. i play the bit on the left when i play it, but yeah i can play both bits technically fine, it was just when i tried to redo them for the album, the new versions, even though much cleaner and tighter, didnt have the same emotion to them.
so yeah of course i can play it live
(interestingly enough Trey from MA always use 2 or more guitars on his solos doing different things and thats why lots of his solos sound very different live as he is only playing one guitars worth of parts)