It's been quite a while since I've seen the MK X in 6mm so I can't recall if the the twist was 1-10 or 1-12. If 1-12 you may have problems with the 100 gr bullets stabilizing. However, if it's 1-10 then I suggest working up a load using H4831SC. Make sure you get the "SC". This is a very good powder for the 6mm, especially with the 26" barrel. I got excellent accuracy with Hornady 100 gr SPBTs at around 3200 fps. I also used fire formed/NS'd W-W cases and WLR primers. With the 85 gr Sierra HPBT I pushed 3300+ fps and it was a rock chuck killer extraordinair. I use past tense as I shot the barrel out. Your Mk X should do fine for Goats, 17", eh? I'd go him if I was you.
Larry Gibson