SolGold Funding Plans, page-24

I see it a bit differently - the oppies are pretty well tracking the heads cent for cent so from half the base they are providing double the return (nearly so in my book).  But look ahead a year and 600 m of economic porphyry copper and gold to say about - oppies and heads will only be a few c. apart but the oppies cost you only half.

I sometimes take your argument when I see a quick trade on the table, but then I want leverage of x4 to x6 to make them worth the risk.

Finally if you trade oppies you must be prepared to let them die if the play (or the market) goes belly up. It happens.