Well, that should be a dandy rifle I will say that. Bullet wise it would be tough to pick a bad one I think.
From the tests I've seen and what I've read the 139gr Hornady Flat Base is a bad mammer jammer. They were unavailable when I got my 708's but are available now. I use the 139 BTSP Hornady and the 140 Accubond from my two 708's but for deer the 140 AB seems a bit tough. The tip on 154 SST would promote expansion and the lower velocity would limit stress. I'm going to order some of the 139 Flat Base for next season just to test out.
Any of the 139 Hornady except the CX or the 154 SST would be a solid choice. Nosler 120-140 Ballistic Tip, Sierra 140's as well.
139 Flat Base:
https://www.bluecollarreloading.com/products/hornady-7mm-139gr-sp-2820?variant=17662501814387