Well your original post didn't ask that and your reply doesn't seem to say that either, I have no idea what peer shield is or how it protects P2P applications as I don't use P2P. Which is why I suggested trying it for your self to see if there was any performance impact.
The p2p shield of avast scans all content, where depending on the file type being downloaded the standard shield may not scan it by default it depends on your standard shield settings. So where there is any element of doubt than I wouldn't rely on a last line of defence.
If utorrent has a function where it calls the anti-virus to scan the completed download then that would ensure it got scanned rather than rely on the standard shield to hopefully scan it depending on your settings. Assuming you installed avast in the default location then this is the file utorrent should call to do the scan, C:\Program Files\Alwil Software\Avast4\ashQuick.exe.
