theres the official OTA updates knocking around online, but just 4.4 update to 5.0. you will need the stock "locked" bootloader with kitkat for it go ahead and you need to sideload it via adb. not sure if you can wipe the rom and install it fresh but there is the official full rom from the dev sites anyway. mine took an hour from start to finish from 4.4 offical to 5.0 OTA. all apps updated and works great. I never jumped onto the pre release as i wasn't desperate for it. I have no critical apps and all mine use current APIs anyway.
sorry if you already know this but im sure at some point this will help someone :)
OTA ROM nexus 5: