To the OP...see if you can find somebody in your area who has a Sargent and will loan it to you. My experience with Sargent is limited to a single test ride. I can't remember the duration...at least 50 miles, probably less than a hundred. I borrowed it from a guy in the local club. It didn't work for me at all. I thought it barely better than stock. I wanted (hoped) to like it. It looks good, price it OK, etc. But that seat and my butt just didn't match.
I bought a pair of used GSA seats, cheap, and they were an improvement over stock, so I rode with them for a couple three years. Ultimately, last fall, I sent the GSA seats to Russell for a pair of Day Long seats. Best seats I've ever sat on. They do take some getting used to, sliding forward slightly at a stop to get the feet down. A small price to pay. Girl friend loves them as well. After several hundred miles, we're not only still comfortable, we're not even fidgeting around on the seats. I chose black, all vinyl, half moon stitching. No regrets about the vinyl over leather.
Good luck finding what works for you.
2014 Road King; 1975 R75/6