Actually, with Tensorflow as a Keras backend, I would expect them to be the same. I am not sure where the performance difference between TF and TF as a backend

Actually, with Tensorflow as a Keras backend, I would expect them to be the same. I am not sure where the performance difference between TF and TF as a backend come from. I do think that pure TF would be easier to scale up over multiple servers etc. but that's only because I don't know how it would work in Keras. Maybe its easy.