Our site is built on Hubspot's COS and now we are thinking of trimming the fat, migrating to wordpress (way more flexibility for design), and then using Infusionsoft for our content offers, emails, etc.
Switching from HubSpot to InfusionSoft is backtracking.
I wrote an article on some of the specific limitations we ran into with InfusionSoft (we ran about 40 million dollars through InfusionSoft over 4 years) that may help provide some guidance in your decision.
Top 10 InfusionSoft Problems http://envoken.com/marketing/top-10-infusionsoft-problems-infusionsoft-wont-tell-you-about/