Does Google Nexus 5 has arm or armX86 or armX64 processor?
The Nexus 5 runs a Snapdragon 800, which is not a 64-bit supported processor. That means you should be going for the arm version of Xposed, and not the arm64 version.

NOTE: You are getting confused with the meaning of x86. In this context, x86 refers to mobile processors made by Intel (the Nexus 5 has an "arm" chip). The difference between "arm" and "arm64" is whether it supports 64-bit execution. There is no such thing as "arm86".  

Currently, there are only unofficial builds of Xposed for 5.1 and higher.