This is extremely inefficient, first off you need 40-50 defence, mystic / god d'hide will do you just fine.
Secondly It shouldn't take much more than little over a week to complete them with 85 magic through curse / alching and 70/75 range at sand crabs.
Strength levels are not needed, you only need 51 agility to complete Regicide.
Hope this helps, goodluck with rest of your journey !