I've tried the hospital pumps too and actually got less milk than with my PIS. I'm only pumping 1 1/5 to 2 1/2 oz every 3 hours. I've also added early AM pumpings since my DD sleeps through the night for like 9 hour stretches. I haven't noticed any changes yet, besides having less yield in the 6 am session.
Thanks for the responses :)