Digital BW, The Print

So I'm curious - 

I keep hearing about people using the Mediastreet Gen4 black with their VM inks in 
order to get a higher dmax and richer blacks.

I also keep hearing about how the ultratones require a photo black for glossy and a 
matte black for matte paper. And so I wonder, why not use the MediaStreet Gen5 
black for both? Would it work? 

Is this a stupid suggestion? If so, why? I get pretty good _color_ prints using that 
black ink on both matte and glossy papers...