Bob thinks he's pretty intelligent. ;-)
It's not easy to tell how Lovey's been responding to the Prozinc. At times, it looks like 1.5u did okay, and so did 1.75u, but nothing consistent that says "that was a good dose". But I know that at the beginning, you found out that the dose you started at was too high after only a couple of days.
Just me, but I think I'd just start at 1u of Lantus, and then give that 4-5 days to settle. If an increase makes sense, then bump it up to 1.25u. Just from watching a lot of cats on various types of insulin, it seems to me that it's always easier to start conservative, and go up if needed. Plus you don't know how she'll respond to the Lantus yet. Some people, especially when they first appear on the board after getting questionable dose advice from their vets, find out the dose was too high to start, and it just seems easier to go up as needed than to go through the exercise of having too high a dose and then having to start over again at a lower dose.