Hardest Manuals only piece?

[andijah]

Doesn't this depend on the player's ability and also on the type of instrument available?
I once played a pneumatic pipe organ that was in such a bad shape that whatever you did, every straight line of semiquavers sounded like badly timed jazzy triplets. So, any fast piece on that organ was hard.

[Barnaby Page]

There are some really tricky passages in the Sweelinck Junges Leben variations - it's rather deceptively simple-sounding in that respect. However, there's also a lot that's less demanding.

[AD43]

What do you all think is the hardest manuals only piece, i would personally but my bet on Tomkins or Byrd.