You see, this is true with Toccatas and other loud or dramatic pieces like opening movements of the symphonies or sonatas or polyphonic compositions like fugues. The large reverberation of the room makes the understanding of the polyphony, harmonic plan and modulations much more difficult. That's why it's best to take a slower tempo, articulate more, and emphasize a little exaggerated phrasing.
However, playing very fast in huge acoustics probably is acceptable not in loud pieces, like Toccatas but softer, playful compositions, such as Scherzos - registered with flute stops and their combinations. When the organ doesn't sound loud and the space in the room is huge, the music seems to flow and can be perceived much more clearly.
If you ever have chance to play a large organ in the room with cathedral acoustics, experiment with the flute stops - take a 4' flute on each of the manual and improvise in a very fast tempo something melodic with a single voice while changing manuals and playing short pedal staccato notes with soft 16' and 8' stops.
If you use suitable modes or harmonies, large reverberation won't be a problem. In fact, you will be pleasantly surprised at what kind of mysterious atmosphere this type of registration creates. The same can be done with any combination of 8' and 4' flutes.
Today's sight-reading piece is Entree de Procession by Edouard Batiste (1820-1876), a French Romantic organist and composer who won the famous composition competition Prix de Rome in 1840. He was an organist at St. Eustache church in Paris where he performed the organ part at the premiere of the Te Deum by Hector Berlioz in 1855 (conducted by the composer).