And interesting on the candidates
As you've pointed out previously the people that will actually make the decision, SNP members, haven't been polled. I'd suspect they'd be more like SNP voters than all voters however.
Looking at the polling I think the SNP may be stuck between a rock and a hard place.
Forbes having rather greater support in the public at large (but don't forget that will include a bunch of people who will never vote SNP regardless of who is leader). But critically she does not have the support of her parliamentary colleagues (at both Holyrood and Westminster) and history suggests that it is very hard for someone to lead a party (let alone govern) without having their parliamentary colleagues behind them.
Go for Yousaf and have someone who will likely command support in the parliamentary party, but may not be seen as the best candidate more widely.
Actually I think the most telling bit of data are the 'don't knows' - that 39% of SNP voters don't have enough confidence in any of the candidates to actually express an opinion should be especially worrying for the SNP.