The rule of thumb (BTW does anyone remember their history classes and remember where that phrase comes from?) when ironing or pressing is -

To use the temperature setting that is the lowest. So in the case of a Polyester and Wool blend use the Polyester setting on your iron. (about 300 °F or 148°C) or about the same as you would for Wool.

The Wool in the blend will do best with steam but the steam will have little effect on the Polyester.

I would press a poly/wool bend and not iron. I would use a dampened pressing cloth. And I would use lots of steam.