The Project Management Institute's College of Performance Management has a periodic newsletter The Measurement News. This month's issue is has several articles about PMBOK and its Earned Value content.

The To Complete Performance Index (TCPI) is very useful for IT type projects that are keeping track of the performance the work being done using Earned Value at the Work Package level. TCPI shows how much better you need to performance to come in on time.

Remember the notion of Velocity in agile makes a huge assumption - the work is time boxed around a constant work effort - a fixed number of people and a fixed number of productive ours per iteration. The dependent variable is the outcomes from that time boxed, fixed effort.

If you project is anything other than time boxed (fixed iteration durations) and fixed work effort (fixed number of people on the team doing fungible work) then velocity is pretty much meaningless. You'll need to have "real earned value" in some way, where Physical Percent Complete is measured against the Planned Percent Complete for a defined period of performance.