Also mentioned in this video about starter motor upgrades at about 11 minutes in…FWIW, some years ago a friend replaced the starter cables on his stock Mark III with larger ones and his previously reluctant (unmodified) starter has worked with no issues at all ever since. So it appears it's a worthwhile thing to do!
West Marine is great source in the US.I have had good luck with 6 gauge marine battery cable and heavy duty connectors.