That's how I interpreted the question (which basically makes it a no-brainer).

Almost a no-brainer. It depends on how many x you think you can add to that valuation in whatever amount of time you are okay with adding it.

Like my sibling post says, my valuation by definition includes the present value of the expected future growth and revenues, in which case you obviously take the 5x offer.

No, because that should adjust your expected value.

It could be 5x of the valuation set at the last funding round, but I agree it's unclear what the OP meant.