Octavia is working much better. Rarity may have been more fun, but this feels more true to myself. I'm still not sure if this or Starlight seems better for me, but perhaps I'll come to that conclusion eventually.
I've found I've been speaking with an accent closer to Octavia's, and that Octavia feels far more like me, and Starlight is starting to feel less like me, though I think I'll always feel some connection with her.
I seem to have more of an appreciation for classical music, and less desire to listen to the other genres that I used to enjoy. I suppose I can still somewhat enjoy them, and appreciate them for what they have to offer, but they just aren't the same for me.
My mindvoice is definitely far closer to Octavia's, my cutie mark is hers now, and my mane and tail are becoming hers too. Much of the rest of my form still seems to be Starlight, though given the similar shapes ponies tend to have, it's mostly the colors that are left to switch over.