I think I finally got it.
Q. Can an investigator use multiple weapons during combat?
A. An investigator can apply only a single bonus to a
test. However, he may use any other effects from his other
The higher bonus to a test. So I can use both the .45 (+3 str.) and the spiritual dagger? (+2 str, +1 will) in the same encounter and use the dagger +1 for the will test and the .45 +3 for the strength test. Right?
According to the FAQ I treated each test individually and didn't have much of a problem until I got blessed/holy? water (discard for +5 str, + 5 will) and was forced to look at the encounter from a global perspective.