There is a bit of a gap in my knowledge on these particular CPUs. Besides the amount of cache, and hyperthreading, these two CPUs should perform similarly right? They are using haswell architecture and are at the same clock speed so I would think they should not be much different.
The differences in cache sizes, power limits, memory speeds, and the fact that the 2630 has hyperthreading add up to quite a big performance gap.
The Atom is designed for low power home/small business servers, whereas the 2630 is designed for more CPU intensive applications. That's why the Xeon has so many more features and almost 3 times the number of PCI-e lanes; It's designed to be a lot more versatile and handle constant large workloads.
Not to mention that the Xeon is Haswell-E and the Atom is Silvermont, not Haswell.