Like you I bought several boxes of Hornady Black, American Whitetail and Match to shoot first. I've got a couple boxes of Federal but I have only reloaded the Hornady cases so far.I have some 140g SST still if you want a couple dozen. Too small of a group to interest you I'd expect but about all I have left. I like them and they have a good BC as well but as you were saying the 140 vs 129 or 123 isn't really worth the game difference/effort and shoot a bit less flat if you're going to hunt. I also have some 129g SP but I can see why you picked the 123 over them as the BC is not great. I tried them first because I had Hornady Deer Ammo (pretty inexpensive) and was reproducing those to learn from before something closer to Hornady Black (also on sale at times and source for my initial brass) for casual paper shooting fun out at the farm.
I thought about getting a box of 129 SST to work up but your info changed my mind and I'll likely get the 123 instead next time.
On cases, however, I'm interested in why not Hornady Cases? Preference to not care for them? Pretty much all I have in 6.5
I also use the Hornady Match die with an insert based on my barrel expansion to avoid a tiny bit of brass stress. (Internet knowledge, not experience, LOL) It will do more than I ever will as I'm too casual but I really like it over my Custom grade dies. Got it based on some of your comments I believe quite a while back.
Came on looking for powder info and noticed the lack of Hornady Case and it caught my eye. Sorry. H4350 bit too hard to get for a casual shooter. IMR4451 was easy to find and I don't believe (insert severe lack of knowledge) that it's that bad or far off what H4350 would do for someone like me. Need to get more but will read around some. Don't mind changing. Big part of the enjoyment for me is working up a bullet.
I enjoy reading what you write though as it give me ideas.
https://www.okshooters.com/threads/ready-to-collect-mo-data-on-6-5-creedmoor.267855/