Digital BW, The Print

Hey Folks,

I've just started out with a digital B&W setup on an Epson 860 with 
MIS Full Spectrum and the Woolf curves. I'd like to try printing on 
Photo Rag but have noted that it comes in two flavors, 188gsm and 
308gsm.
I would appreciate it if someone might shed some light on the 
advantages and disadvantages of using either paper and how they would 
work with a printer like the Epson 860.

Thanks in advance,

Mark