Is there somewhere for me to go and download info on gamut sizes for various Epson printer/paper combo? and compare these to color spaces like Adobe 1998 or Colormatch to determine if the Epson gamuts fall within these spaces?
Off hand I don't know of any sites that have a capability for you to load a specific profile and plot it over another. You can do this yourself in the ColorSync utility on the Mac or with a product like ColorThink from Chromix (among others).
I haven't looked at a 4000 profile in years but I can almost guarantee there are colors that plot outside of ColorMatch RGB. That's not a stretch. The newer K3 and even more so, the HDR ink set exceed Adobe RGB (1998) gamut in some colors.