Rails view generation is shockingly slow. I would definitely cache partials, I just wouldn't run Redis to do it if I could help it!
Rails is basically the worst case framework for our model, so we were excited when we got it working. You still have to work hard to make Rails fast, we just give you the last mile for almost-free.
I guess I misinterpreted when you said "And you might find out you don't really even need a cache. Rails + Postgres read replicas are pretty dang fast."
You actually meant, you might not need a CDN cache... if you have some other kind of cache (which btw ideally isn't redis if you're using our model anyway)... because Rails actually isn't pretty dang fast at all?
Rails is basically the worst case framework for our model, so we were excited when we got it working. You still have to work hard to make Rails fast, we just give you the last mile for almost-free.