I considered adding some suggested models to my original reply to your question, but I didn't because I don't have much information to go on.
The answer is, it depends. It depends on the number of users behind the firewall. It depends on what software blades (how much security) you're planning to enable. It depends on your needs/desires. Do you really want/need to be able to max out your 400Mbps Internet pipe? Are you hosting any services behind your firewall such as email, web servers, etc.? Are you using VPN? Site-to-site or remote access? Is site/location critical, or critical enough that you need failover/redundancy? If so you need to consider a cluster of firewalls. This will pretty much double the cost of any firewall you might put in place. Do you have other Check Point firewalls or is this your only one? Do you have an existing Check Point management server in place? If not, are you willing to bear the cost of putting one in place? All these things factor into a sizing/appliance decision.
If I had a Check Point management server already, I would probably look at the 3200. It can do up to 385Mbps of NGTP throughput. Not quite maxing your 400Mbps circuit, but close enough in my book. If you really want to ensure you can cover that 400Mbps circuit with NGTP protection, then you've got to go with a 5100 at minimum. Appliances 3100 and larger require a Check Point management appliance. They can run in standalone mode, where management and firewall run on the same box, but in my experience virtually no one is ever happy with this configuration.
If I did not have an existing Check Point management server and needed something with a similar locally managed interface to the existing 1100 series, I'd look at the 1490 or 790. With these however, you are only going to get around 220Mbps or 330Mbps (respectively) of NGTP thoughput, so about half to three quarters of what the upgraded circuit could handle.
I'd probably also look at the 910 and its 350Mbps of NGTP throughput.
All of the above would be on my short list of appliances to look at given the single requirement that you want to upgrade to 400Mbps circuit. However, based on the answers to the above questions, my recommendations might change.