Digital BW, The Print

I have shot a few rolls of Portra after using Super XP2 regularly. It 
seems to scan very nicely, but I have two questions and an 
observation.

First, I shoot XP2 at 320 rather than 400.  Is that common practice, 
or do people shoot Portra at its nominal speed of 400? Second, and 
more subjectively, XP2 has a "creamy" or flowing feeling to it that 
seems to be missing from Portra.  Has anyone else noticed that?  
Last, based on two rolls -- not a large sample -- it seems that while 
Portra scans more easily than XP2 the prints I get back from the 
processor, which I use only as contacts anyway, are more contrasty 
and have a more limited tonal range than XP2.  

Steve