Blundering around on NASA, I picked up on Sunspot 720, which not only produced 5 huge solar flares, but delivered the last one in 30 minutes. From 8 light-minutes away. A bit of quick calculation reveals that the storm was thrown at over a quarter of the speed of light!
Here’s a closeup of the sunspot itself:
“[Coronal Mass Ejections] can account for most proton storms,” says [RHESSI mission head Robert] Lin, but not the proton storm of January 20th . He theorises that it was channelled along the Sun’s magnetic field lines. But still... faster than 25% of c! An interesting article.