This may be the largest thing the human race has built (bearing in mind it doesn't exist), but it won't be the fasted. Whilst it is important to note the frame of reference (relative to the Earth, the surface of the Earth, the Sun, other planets etc.), a speed of 30km/sec would not qualify. The Helios probes approached 250,000km/hr or about 64km/sec at their closest approach to the Sun. In addition, the Gallileo probe reached 48km/sec when it was intentionally destroyed plunging into Jupiter. Even if measured against the Earth as a frame of reference, these will still beat this proposal.
It might be said that using a gravitational well is cheating, but at least these craft were built..