Hey @ryanrozich!
We ran into the exact same problem. Your approach of attaching A/Bs as custom contexts to page views looks good to me - the issue you’re seeing with the data modeling step is caused by rebuilding the entire table on each run.
Christophe has a great tutorial on how to make these models incremental. Using this, we were able to reduce our web-experiment model runtime from 1.5h to 5mins.