I also have a p4xi, and my impressions are favorable of it. The image quality of the scope is very good, and as others have said it performs much better than other scopes sub $1000. As Koshkin (Ilya) has said, the scope is a raging bargain for the current price from Doug.
One note about the scope if you are concerned with the magnification range, is that scope with lower magnification with a higher level of image quality is much better than a high magnification with lower quality image. Having said this, I would take the Steiner over the 5-20 razor. The p4xi image quality is a step above the 5-20 razor, and closer to the 4.5-27 gen 2 razor.