I had a Delos and upgraded to the Kleos. The Delos is a great cartridge for the money, and could easily sell for 500 more and get away with it. It is a newer design than the Dorian. I traded a LydianB , I have never heard the Dorian but I am sure it is good too. I love the Lyra sound, but if you are willing to spend the extra, why not get the latest, newest design? You never said what he is charging you for the Dorian. If it is a great deal, you can get it now and Lyra has a good trade up program. I got 700 for my Lydian that sold for 1000 new and I had paid 900. So that could let you try both over a period of time.
Just my opinion, not to offend anyone else, only answering your original question.
Just my opinion, not to offend anyone else, only answering your original question.