The mash temp and pH effects are pretty complex and interrelated.
The table below (from "Malting and Brewing Science" Briggs, Hough et.al)
shows that the greatest amount of phosphate buffers are also
produced at the protein rest, (because it the best temperature
for phytase activity), this in turn effects the pH. The
amount of protein broken down to permanently soluble protein
is important because that is what the yeast eat, and because
it won't be precipitated with tannins (meaning clearer beer).
The pH will affect both the amount of harsh-tasting tannins
extracted from the husk but also the amount of precipitation
(haze) that is produced (because of precipitation with the
proteins). pH also affects exract, as the greatest
extract occurs between pH 5.3 and 5.9.
Highest extract 149-155
Highest yield of fermentable extract 149
Highest yield of permanently soluble nitrogen 122-131
Highest yield of acid buffers 122-131
So the protein rest has many effects, whether it will have
more effect on a homebrew than say, fermenting at an
improper temperature, or not oxygenating, will vary from
yeast to yeast and recipe to recipe and process to process.
A protein rest in general seems like a good idea though.