I believe I've read that the real speed limit is 100 kilometers per second. Any faster any the electron-shell stability of most atoms will become significant enough to induce heavy thermal increases.?
(Essentially, you will cook as if in a microwave oven,,,)
As far as "going fast" is concerned, the easiest solution would be to build a large mag-lev train in space. It would be like a large particle accelerator so you could get the ship up to just below the speed of light as it circled around, The problem, of course, is the 100kmps limitation as originally stated (if true)...
Well, the other problem is "stopping"...