I dont know
But, I'll try and offer some guidance since youve been ignored by the folks that actually know what they are talking about.
The "synergy" of Pulm and CCM seems to be that 1. the skillset has a lot of overlap (PA catheters, chest tubes, vents...), 2. The side of CCM which is more than just Internal Med on steroids (which most of it is), seems to be a lot like inpatient pulmonology. When you're in critical condition, You have to support the ABC's. The Circulation part is dependent on the Airway and Breathing. It seems theres a bit more more that can be fine tuned in physiology involved in maintaining adequate oxygenation and perfusion than there can be in keeping the heart beating
Sepsis is a huge part of CCM, and Im sure that knowing your ID would help. However, the skillset doesn't overlap like Pulm/CC. You'd be learning the entire skillset in your CCM fellowship.
Lots of CCM programs look for specialists in other fields such as Cardio, ID, EM.
As far as balancing your practice. You can always work as little or as much in each of your subspecs as you want. Plenty of people attend in the ICU 2-3 days a week, and to Pulmonology consults on the other days.