All of the Raspberry Pi devices perform comparably similar with respect to Ethernet. They all have a dedicated Ethernet chip which is hooked up to the SoC via an external bus. Performance tests usually show that with the recent version you can actually really get to the 100MBit/s on wired Ethernet, and up to 40MBit/s via wireless. There are users who found that you can go up to 200 MBit/s if you buy a good (= expensive) USB-to-Ethernet adapter, but I doubt that it is really worth the effort.
Expect the Ethernet chip (marked with M1) to go even hotter than the SoC (M2) at full speed.
Encryption performance is an interesting question: Modern "normal" CPUs (like x86_64) have no problem at all, because the integrate circuits that are specifically designed to compute crypto-stuff. Well, in the world of ARM everything is different and I wasn't really able to draw conclusive information from the datasheet of the SoC used on the Raspberry Pi. It seems like CRC32 is implemented native, but for the rest this is left open (could even be that it is in there, but does not work with Raspbian).
I tested the VPN performance using OpenVPN + Raspberry Pi Model B (700MHz single core) and ended with about 9MBit/s performance. Repeated the same test with a Raspberry Pi 3 Model B (1.2GHz quad) and got about 13 MBit/s. So not really high-performance but in good agreement with what you would expect from there devices. 2048 keys.