Digital BW, The Print

In his specifications for using MIS-VM inks (1200) Paul Roark 
suggests that the print profile (in print with preview, advanced) be 
set to "same as source."  I find that setting it to "color match RGB" 
seems to provide somewhat more "snap" to the image; a bit more 
contrast without increased posterization or negative impact in 
highlights or shadows.  Am I missing something here?  Does this 
setting degrade the image or have other negative impacts?

Steve