Right, let's clear some things up here:
In oil viscosity ratings, the first number is it's performance when at operating temperatures. So saying a 0W oil helps cols starts is nonsense. The second number is it's performance when cold, so saying a 30W oil is thinner than a 40W oil is only stating the obvious.
While thicker oil does necessitate extra drag, it is miniscule compared to the effort required to turn two camshafts. Next time you've got the belt off, try it. The starter motor extra drag when cold is caused by metal contraction, but even that doesn't really compare to the effort to overcome valve springs. The starter motor is unaffected by oil viscosity. This extra strain 40W oil puts on a starter motor is imaginery, as my 188,000m motor has verified today.
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