I dont personally use antivirus. I run multiple os's in a quad-boot setup. Any downloading of 'suspicious' files I do within a virtual machine, and only after thorough testing do I transfer to my main OS's. (just for clarification win10, OSX 10.10.5, Ubuntu 12.04, kali 2.0 on a gateway laptop)
Nexus 5 all the way!! rocking nethunter 5.1 on top of a custom, unreleased slimmed stock rom. Also running a custom, unreleased kernel, enabling a whole bunch of usb wifi drivers, filesystem compatibility (eg ext2,3,4 ntfs, etc.) and overclocking UP TO 2.9 Ghz. O hell yes 
Too anyone who wants to try the kernel.... heres a link. ANDROID 5.1.0 ONLY! also 2.9 Ghz is cool for a quick test and for bragging rights, but NOT a stable OC for general use. it will overheat. I use 'devil kernel manager' to set cpu OC.
https://mega.nz/#!H9hAzCiD!J-qlljwabSVwD0u5FyGa-ekZdCNv47VwvxrD50kvdAk
enjoy
edit
Just added it to xda forums http://forum.xda-developers.com/google-nexus-5/development/nexus-5-hammerhead-5-1-0-nethunter-oc-t3274880
/edit
Too anyone who wants to try the kernel.... heres a link. ANDROID 5.1.0 ONLY! also 2.9 Ghz is cool for a quick test and for bragging rights, but NOT a stable OC for general use. it will overheat. I use 'devil kernel manager' to set cpu OC.https://mega.nz/#!H9hAzCiD!J-qlljwabSVwD0u5FyGa-ekZdCNv47VwvxrD50kvdAk
enjoy
edit
Just added it to xda forums http://forum.xda-developers.com/google-nexus-5/development/nexus-5-hammerhead-5-1-0-nethunter-oc-t3274880
/edit
You seem to know what you're doing. I like to see that. XDA is a great place.
Can't wait to fiddle with Marshmallow.