Check Point does not publish the exact hardware specs of their appliances.
That said, there are unofficial sources of this information, such as what you linked to above.
Open Servers and Virtual Machines have different performance characteristics than Check Point appliances, even when the exact same hardware is used in both cases.
The Hypervisor (for VMs) and hardware drivers in question will play a huge role in the overall performance.
You can try to get a Open Server appliance with similar specs to a 5100/5200, but:
1. Performance on Open Servers is not tested nor guaranteed.
2. For the server to be supported, it must be on the Hardware Compatibility List.
That said, using similar hardware usually provides similar results.
For VMs, you are not going to get the same performance as you would get on equivalently sized bare metal, particularly as you start increasing the core count.
I would work with your Check Point SE on sizing VMs.