Have you tested this? I ask because under the hood, Rails is using Faye, and Faye is using EventMachine.
About 10 years ago I load tested Faye vs. Node in a websocket scalability test for a websocket based chat app I was writing, that, funnily enough had a polling fallback. We had scalability needs up to around 10k or 20k simultaneous connections if I remember right and I wanted to know their ceilings before we wrote the real code and invested in either.
Faye kicked Node's butt on simultaneous connections and throughput. Node fell over while Faye was still going. Eventmachine, which Faye uses, can scale like nobody's business. It IS an F16.