So far as I know, there is no "official" size chart.
Save yourself a HUGE headache and get fitted somewhere. I have had both SP Teri and Harlick, and they weren't the same length. If you try to just order them based on a size chart I can almost guarantee that you will end up disappointed. There is so much more to it than just the length. Depending on where you are located you should be able to find a pro shop that knows how to fit for different skates. Additionally, both skate makers travel to competitions to do fittings. That may be an option for you too.
It really is worth it to spend the time/money to make sure they fit right.
Harlicks v. SP Teri just have a different feel to them, at least in my opinion. I always thought my Harlicks were warmer, and had a bigger toe box, but I just like the snug feel of my SP Teri boots better. I think the heel on the Harlick is a bit higher, which can change your balance point slightly. I actually think that the length of the boot may be the absolute least important feature. I would much rather have a skate that fits perfectly around my heel and instep. And you aren't going to get that kind of fit from reading a chart.