I'm on Rogers in Canada. I'm reporting my findings and hopefully this could help.
When I forced my Nexus 5 to only use LTE bands and nothing else. I was able to go to places where the phone would switch to 3G 70% of the time and back again to LTE on the Main Floor. I was able to take it one step futher and headed for the basement where LTE would not exist normaly. With no bars the LTE service continued. 10Mb/s down. And so I went further and started covering up the antenna with my hands and I was down to 5Mb/s down. Just as good as 3G. And with my hands covering the antenna I also used my body and the speed went down to 2Mb/s and stopped working as I was curled up to my hands that was covering my Nexus 5 while in the basement but as soon as I uncovered and a few seconds / minute later the LTE service came back while i was still in the basement.
I don't know if it was a consistent speed but better then 3G with no bars on the LTE side of things.
The Nexus 5 is interpreting the LTE signal wrong and changes to 3G mode too soon.
I used Network by Philipp Mangelow to change my network settings.