Go to an engine bolt, ring terminal contacting (scraped clean) engine case, with an engine bolt frame to engine contact area also scraped clean (does not have to be the same bolt as the cable). The only high battery current is for the starter motor which grounds directly to the case so you want the battery negative cable to go to the case and avoid an extra frame-case connection.
Frame connection will work OK but you have an extra connection to cause problems.
The stock cable is over spec for the actual starter current and that gauge is adequate for an extended length to a relocated battery, unless you put your battery in a trailer. Be very careful with the positive cable, add sleeving where it contacts the frame. If the insulation wears through from vibration (the heavy cable will vibrate and flex as you ride) and the core touches the frame ... very exciting, not in a good way.
