Archwizard’s Might does not appear to add an additional 10th level spell slot on a 20th level wizard.
Worth noting that the character was almost impossible to finish due to severe lag. Every selection took a minute or more, sometimes the page just hung and I had to close the tab and try again.
Thanks for letting us know! We haven’t finished working through every single feat yet, so I suspect this is one we just haven’t gotten to, but I’ll make certain this is on our list to take a look at. 
Could you please share your character with me here to take a look at with the team?
Unfortunately, no. I’ve since deleted it. I can rebuild another if you’d like but it won’t be exactly the same.
For the record, it’s been my suspicion that the spellbooks are what slow down characters, though it could just be coincidence with some other factor slowing server performance while I’m building a caster with a spellbook (I have only built a few). I can’t say for sure yet. But I intend to continue building characters. Hopefully I’ll see a more clear pattern.
That won’t be an issue, we can build the character on our own then. It’s helpful to see what the engines are doing behind the scenes while troubleshooting issues.
We have plans to address performance issues as we continue developing the Pathfinder character tools, but it’s definitely true that having more things to load on a sheet can slow load times down a bit.
This should be fixed now!
Awesome, thanks!