[Pillow]

As Jake said, it probably will not read that much differently from the sump to right after leaving the oil cooler on a good engine.

If you have a marginal engine that does not cool well in the heads and generally runs hot I bet the varience from the sump to after the cooler (provided the amount the cooler can actually cool the oil) will vary more. Crud engines make heat in the heads instead of cooling there.

In summary the sump plate is good enough for what you probably need, but after the cooler is the best spot if possible.