Azure Monitor for VMs - Log Queries

Jonathan Rossi you're right, there are 2 separate performance tables.

Perf is still the default table, it holds the performance counters you chose to collect (at the workspace level). The previous version of VM Insights used it as well. The new version of VM Insights now collects performance metrics into the InsightsMetrics table. The sample queries that you see for any VM resource, on its Logs page, use the Perf table, regardless of the VMInsights version you install.

If you're concerned about having both Perf and InsightsMetrics, read this FAQ entry.

The link provided on the first reply to your question (to sample alert queries) has the best examples to querying InsightsMetrics I could find.