just picked up a P3. I know it does not have a THD indicator. On my old PPP, THD in was 4.0+, THD Out usually 1.0 o less. Can I expect the same level of performance with the P3?

You bet!

You will both obtain similar reduction in THD, likely better with the P3, but improved performance over all such as lower impedance. I am certain you will be pleased.