Here are what I consider to be my metaphysical assumptions:
1. There is an actual reality external to us that exists. In other words, we're not in the Matrix.
2. Other people are actual, independent, sentient beings.
3. As a group, we can accurately sense that external reality. Particular individuals in particular situations may be mislead by their senses, but when there is a general consensus, for example, the sky is blue, that general consensus is usually accurate. In other words, we're not all having the same delusion.
I reject your classification of the two possibilities that you offered as being metaphysical. They are statements that purport to describe reality. As such, they are subject to scientific investigation the same as any other statement that describes reality.
Second, the universe is very different under the two metaphysical positions above.
You say that, yet you fail to propose any observational distinction that anyone could use to be able to tell which of the two universes we are in. Can you propose such a distinction? Or, can you explain why we should care about which of two statements that have no observational distinctions between them are true?
Ridicule is the only weapon which can be used against unintelligible propositions. Ideas must be distinct before reason can act upon them; and no man ever had a distinct idea of the trinity. It is the mere Abracadabra of the mountebanks calling themselves the priests of Jesus. -- Thomas Jefferson
For we know that our patchwork heritage is a strength, not a weakness. We are a nation of Christians and Muslims, Jews and Hindus -- and non-believers. -- Barack Obama
We see monsters where science shows us windmills. -- Phat