SD HC Memory Card Speeds

What is the difference between Class 4 and Class 10 SD HC Memory Card speeds ? I just copied a 3G image using Win32DiskImager to two 16G SD HC cards one Class 4 and the other Class 10 (but labelled 30MB/s) both from ASDA.

The speeds / times were as follows

  • 16G C4 averaged ~ 4MB/s and took ~10 mins
  • 16G C10 averaged ~ 10MB/s and took ~4 mins

So maybe it really is worth paying twice the price for 2.5 times the speed !