Hi,
Looks like people have things under control for the moment? BJ sent PMs to some of us and asked us to drop by.
Just a couple notes. Some folks have already mentioned this, and you verified it, that NPH is a U100 insulin. I think but not positive, that pretty much all of the "human insulins" are U100 strength. Prozinc/PZI comes in U40 concentration but they are specifically designed for use in cats, not humans.
From "watching" many other cats go from one type of insulin to Lantus, the usually rule of thumb is about 70% of what they were on with the old insulin is suggested as the starting dose for Lantus.
That said, given that you don't have a lot of data collected yet with the N type, I'm guessing that "conservative" would be the way to go. 70% would be 1.75u, but others have already suggested 1.5u or 1.0u. Probably better to start low at first and get some data to find out where to go from that point forward.
Right now, the numbers look fine, but it is early in the cycle. Another point would be that due to the way Lantus works, especially at first, it's not too often that you would see a kitty on his first dose of Lantus drop like a rock like they would on a short lasting, quick acting insulin like N.