Have owned both Sako's and MRC's. All left handed. All have fed, fired, and ejected with zero issues. Neither would be a bad choice. Things you might want to consider:
1) My impression, off the shelf MRC sporters might be a little heavier than than comparable Sako's. That could be a positive if you are shooting a thumper. Could be a negative if you are climbing a sheep mountain.
2) Stock ergos vary. I really like the new MRC X2 synthetic stocks. Not so much the MRC ASR wood stocks from Boyds. Sako AV style wood stocks are O.K. for me. I have had a couple MRI Mountain Eagle rifles built on Sako L691 actions in HS Precision stocks that I could shoot all afternoon without feeling beat up.
3) Safeties: MRC uses the Win M70 3 position swing safety that locks the bolt, if that is important to you. The left hand Sako's that I have owned still had a right hand rocker safety. Sounds counter-intuitive to use a RH safety on a LH rifle. But actually requires less movement to release the safety since you do not have to move your thumb back to the left side of the action to manipulate the safety.
I would gladly hunt either one given the chambering and stock of my choice...
