There's one more thing you need to consider - all those numbers are MAX when CPUs have been pushed to the limit. In your daily life you don't want your appliance running 99% CPU and having no headroom for any "bumps". Half the numbers for realistic approach.
To give you real life example from the same series - 5900. We run all blades but threat extraction and box at 100% CPU probably would meet the datasheet numbers roughly 7Gbps. But I would never allow to go that far. Normally we start planning upgrades at 50% CPU as it gives us sufficient time to plan and implement.
Pure FW throughput - I actually never seen any of appliance getting anywhere near advertised numbers in real life I'm afraid. We have bunch of mid and high end appliances and at best I would say we could squeeze out about half of advertised FW throughput.
With Checkpoint it is a big "guestimation" when it comes to sizing. All depends on traffic mix you have and your own experience / gut feeling. 🙂