NikT: I pay close attention to these as part of my job. One thing to bear in mind is that while most vendors will advertise 64bit capability at the chipset level (Particularly with newer Mediatek SoCs), this means nothing unless the device runs Lollipop out of the box with full AArch64 compatibility.

No vendor has to date converted a device from 32bit to 64bit via a Lollipop update, so avoid devices that ship with KitKat if 64bit is a selling point for you - This would require a full wipe and is technically possible but I'm not aware of anyone who's gone to the trouble. 64bit is still a bit buggy & unstable on Android without the optimisations the likes of Samsung & HTC have implemented on the S6 & M9, so one to watch out for.

The LTE bands to look for are: Band 3, Band 7, & Band 28, which correspond to 1800MHz, 2600MHz, & 700MHz respectively. Most Chinese devices that do have international variants will use Band 20/800MHz instead of Band 28/700MHz as they're targeting the European market - the ASUS Zenfone 2 is a notable exception.