Nathan -- Shooting 150 fps using a heavy 13 gpp arrow is not that bad. If you really were getting an extra inch or so in your draw with about three more pounds of draw force and an inch of extra power "stroke", you would get more velocity. You can kill anything in North America or Europe with your setup, especially if you can repeatedly hit the same point at 20 yards.
Margly -- I can guarantee you were not overdrawing the bow, even at your 31" draw length. If you order another Shrew, you might want to consider a Classic Hunter, which will actually accommodate a longer draw length than a 60" Super Shrew. If you don't believe me, ask Ron LaClair or Gregg Coffey. The only Shrew I know of that might be more comfortable for you at your long draw length could be a Shrew Model T, but you sure don't need it, and it would eliminate most of the advantages you would want if having a shorter bow were one of your objectives. BobW here on TradGang has a 32"+ draw length and has no problem with his 56" Classic Hunter. He has repeatedly written about that in his posts.
Allan