Mario -
Don't bother with a single speed sanders. You are a knife maker, hobbyist or not, so get a knife-makers sander. Since you work with expensive stuff, spend a little more, get a variable speed sander, same as you saw at Devin. Don't buy retail - buy the frame from trugrit.com and motor and VFD drive separately. I saved myself $300 over the retail price buying motor and VFD on Ebay, both new. You won't regret it. Get 1HP motor 3450rpm. You can do metal grinding on it too, particularly thinning tangs, flattening spacers, and more.
I made a vertical disk sander same way. Total cost for a motor, a VFD drive and a disk was in the area of $240 shipping included (motor was 3/4HP). All top quality American made products (KB Electronics Drive, Baldor or Leeson motor). Drives can be bought for much less what I paid (I like KB Electronics and Baldor, which KB might be the OEM).
M