Hi Tiffany,
I might be wrong and you can test it but when you run the smart campaign you will get leads which you can export. When there are 3million leads you cannot import them to Excel because it's limited around 60000 records.
When you want to see the different values and there are not too much you could also filter for the field, click in the value field and Marketo will display different possible values.
After that you could run several smart campaigns to get the numbers on how many people have the different values.
Best regards
Steffen