Thanks for the great responses. I've synced 1MM before and it took about 24 hours. Just to be clear, these leads/contacts will be updating a SFDC field. I will run them through campaing#1 first, which is resetting a score. They have to complete that before I can begin campaign #2 & #3, which are scoring campaigns.
I do know my API limit (about 750K). I've done the calculations for the API requests and I think I'm in good shape, so I'm not too worried about maxing out the AP,. 1 campaign is about 10K API calls. Marketo support seems to think it could take a good 3 days.
I do like CRM fusion, but I don't have a subscription right now. As an alternate I am using Dataloader.io to update some additional fields. Has anyone used Dataloader.io and know the record update limit per API call? I know it's a lot less than Marketo, but I haven't gotten an exact figure. For Dataloader I'd be running tasks w/bulk upload.