Converting the numbers to decimal makes it easier to see which can be used:

# egrep "^ .*|System RAM" /proc/iomem | sed -e 's/ : / /g' -e 's/-/ /g' | awk '{;printf("%d bytes to %d bytes (%d M to %d M) - %s %s\n", strtonum("0x"$1), strtonum("0x"$2), strtonum("0x"$1)/1024/1024, strtonum("0x"$2)/1024/1024, $3, $4)}'