. . . . Wondering about the other options, Sargent, adcox, etc.
Still trying to decide on panniers too.
Those two are extremely subjective. Travex is right, start with the seat leveling; good place to start. I didn't notice a big difference, but it didn't make it worse. My candy ass can't take real long rides. I had an ST1300 that had a gel OE styled seat. The gel made a huge difference. There are plenty of guys here that have changed out their seat, and can provide better opinions/advise.
If you're going to use your panniers a lot, then OE is probably not what you want. The main issue being the locking mechanism. I don't use mine a lot, and I like OE. Minimal framework, good capacity, and looks. Once again, there will be plenty of advise on which ones to get.
Good luck.