I'll just add this.
I used to be a big mobil 1 user and I used it in both my Explorer and Mustang.Then when they started changing their formulations,I grew tired of paying a premium for an oil that was no longer a premium oil IMO. I then switched my choice to Amsoil,which served me well and have no regrets what-so-ever.Like yourself,I recently decided to try out Redline,for a run during the winter months,as it has superior cold flow properties.If I like it,I'll stay with Redline.
If I was you,I'd use up what you have of the mobil and then when that stash is used up,I'd switch it to Redline,I mean lets face it, A mustang likes to be hot-rodded every now and then,and if your like me,you want the best for the baby,just my thoughts / opinions.