Hi ScotJ,
I work for HP and I'd like to provide you with some additional info on Enhanced Productivity Mode (EPM). You are correct that EPM is available on the newest series presses, which include:
» HP Indigo 7600 Digital Press
» HP Indigo 5600 Digital Press
» HP Indigo W7250 Digital Press
» HP Indigo WS6600 Digital Press
» HP Indigo WS4600 Digital Press
» HP Indigo 10000 Digital Press
» HP Indigo 20000 Digital Press
» HP Indigo 30000 Digital Press
It is not available on your HP Indigo 3050.
You are also correct that the EPM mode produces color jobs using only three inks instead of four. The CMYK job is sent to the print server and is converted to CMY there. Prepress work is not affected and jobs are prepared as usual. EPM results in 33% faster output speed and most printers report little to no noticeable quality difference on most applications.
If you'd like to read more about EPM, here is a link:
http://h10088.www1.hp.com/cda/gap/display/main/index.jsp?zn=gap&cp=20000-15999-16005%5E374026_4041_100__