The Langematik was a nice watch indeed. You're right, they do make a Saxonia Automatic. The reason why the 1815 was chosen was because the 1815 has a lower starting price point than Saxonia automatic. So why not a manual Saxonia you ask? Well, I chose the 1815 because it was a "larger and more modern" size. Basically, I went for what I thought was the closest match to the PF from Lange, Vacheron, and Patek.
It's funny, we now consider 10K CHF to be "reasonable" it's amazing that things have changed so much over the years.