@supernova7005: I know it would take more tham 3 days to walk the entire Pennsylvania but is Pennsylvania anywhere near the size of a small country? No. Just because you believe the OBD has no credibility doesn't disprove the calc.
@FormerCrimsonKing: According to google maps, you can walk 215 miles (or 340 km) in 3 days. This, they have got using an average speed of 3 miles/hr. And yeah, its larger than a small country like belgium
OBD's calc is invalid because they have based it on pixel scaling, rather than trying to understand the author's intent. We know very well that mangaka don't draw to scale, so the information given in the manga is always more reliable than scaling sizes by counting pixels.
If you want a better calc, here you go - http://lounge.moviecodec.com/vs-general/the-speed-of-lanza-del-relampago-158325/ (they've calced both its size as well as speed based on the information given in the manga alone)