[resto3]

I think that viscosity does have somewhat of an effect.  I often direct fire step mash on my stove with grain bills of up to 20 pounds.  While adding heat to the mash I am constantly stirring gently to avoid scorching.  I observed that as the temp steps move up it get easier to stir so I would rather think that the higher mash out temp does aid in lautering.  I could be wrong though.

[tomsawyer]

I've seen a bump in efficiency with a mashout, but it comes with a consequence of slightly increased FG.  My theory is that the mashout stimulates a brief burst of alpha amylase activity as the temp comes up through its optimum range.

As for complete conversion, I guess I'm not crushing quite fine enough or something because I don't typically get results that are consistent with 100% conversion.  Even when I mash for 120min it doesn't seem like I get 100%, I don't know if you can expect that from a mash that favors beta amylase.