Thanks for pointing me in the right direction. That whitepaper has helped quite a bit. It does look like the tabular models, currently, are only about 50GB in size total.

After further investigation it looks like the Excel workbooks that are querying the models are hitting a tipping point of performance after selecting 6-7 slicers, at which point the data refresh takes 2-3 minutes. We will continue to look into this.

Thank you!