Last March I flew to Paris on a CO ticket, with outgoing on CO metal & the return on AF. I was upgraded using miles on both segments, but found my return (while BF appeared fairly empty) took much longer to have my upgrade cleared (7 days prior to my flight). CO told me that is not uncommon, since they must clear any upgrades with AF and they are not as quick to do so.
But more importantly, is there a reason you want to fly AF??? I found that portion of my flight very disappointing. If you check the AF threads you'll find some interesting comments from those who fly them frequently.