Metrics w3cvc is for Visually Complete and w3cspidx is for Speed Index. Supported for raw, trend, and table calls.
Often times, you may want to compare the data retrieved through REST API with the data displayed in Portal charts to validate if you are querying for the right data. Please note that the data retrieved through REST API is in UTC. And the time zone for your account might be different.
For example, if your account time zone is in UTC-4, the same data point is labeled as test time of 5:00 AM (UTC) from REST while in your account it is labeled as 1:00 AM ( UTC-4).