Re the request for opinion, without knowing the full set of circumstances any opinion as to the presence of infringement would just be shooting in the dark and not of any real help to you. As noted above, the infringement analysis is pretty fact intensive and can be rather complex.
Having a better understanding of what goes into an infringement analysis, however, may be helpful.
First and most important is to understand that in the US trademark rights depend on
use of the mark, not registration. You say the other company had a trademark and talk as if you don't, but I wonder if what you mean is that they have a
federally registered mark. If their registration is recent (within the last 5 years) but you started using a conflicting mark earlier than they did, you could have superior rights even if you haven't registered yours.
For example, if you started using XYZ as your brand of groundhogs in 2007, and someone else registered XYZ as a mark for groundhogs with the PTO in 2009, you might be able to get their registration canceled, providing your 2007 use was in interstate commerce and they didn't start their use in interstate commerce till 2008. Or, again, say they started using XYZ locally in Punxsutawney, PA in 2005 but didn't go to interstate till 2008. Even if you didn't begin using your mark till 2006, you might
still have superior rights nationally if your business went national before they expanded beyond Punxsutawney -- provided you were someplace other than Punxsutawney to begin with.
And even if you are only still operating locally where you started in Podunk, Iowa, you could have the right to keep using the mark in your local area even though they get the mark for everywhere else.
And that's assuming the marks are identical and used on identical goods.
Now, as for "likelihood of confusion," your apparent confidence that the minor differences can make marks not likely to be confused is unfortunately misplaced. In determining whether marks are confusingly similar, it's not a side-by-side comparison. Rather, courts and the PTO try to get inside the head of the relevant buyers who may see one mark here and the other at later time there. How likely is it they could mistake one brand for the other under circumstances typical of such purchases? The similarity of the goods or services also plays into this analysis, as well as things like channels of trade and how sophisticated the buyers are. In essence, the question comes down to whether buyers buying those sorts of goods/services are likely to be confused as to whether the junior user's goods/services come from the same source as the senior user's goods/service. If so, then the junior user has to give way.
I found a site a today which might be helpful. It's at
http://www.gimmelaw.com/trademark-law and gives a pretty good summary of some of the basics of trademark law. (I've noted a technical error, but on the whole it's a good explanation.)
Good luck.