I did notice some difference when I switched from the single insulation of the Pro575 to the double insulation of the Gen 2 Ironwood but I have never altered a cook on either because of it. Traeger's excel at low and slow and if it happens to end up a tad slower because the outside temperature is lower or you use a few more pellets it just means there is a bit more time for an extra beer (or on Christmas Day mulled wine!) before the food gets to the correct internal temperature!
Colder temperatures are an extra incentive not to open the hood to have a peak!