You can perceive yourself to be travelling faster than light. I think 71% cee is the threshold when the universe will appear contracted sufficiently that it will seem like you are going FTL.

Even more important than the propulsive energy requirement is how to avoid colliding with space dust at that speed. At 10% cee subatomic particles (protons and other kinds of ions) hitting the hull of a ship would flood the interior with gamma radiation -- not healthy. Using some kind of electromagnetic shield to deflect them would also be problematic because not all of the particles would have a charge.

I think the real breakthrough would be finding a clear path though space. It would be neat if we could do some sort of artificial "expansion of the universe" technology, and go right through any matter that gets in the way (takes some imagination).