PS 460/500 are farm versions of professional PS 4600/5000.I know I had read it somewhere on one of their sites, but I wasnt sure which saw it was, I was thinking it was the 510. I basically learners 5100 and 5105 were the ones to get in the 50cc class.
PS 510/5100 is just US version of 500/5000.
PS 4605/5105 are newer versions of 4600/5000.
PS 550 (EA5600F) is relatively new farm saw with - afaik - no corresponding professional model.