We find that http://browserbench.org/Speedometer/ -- which is what v8 is optimizing against now -- is extremely close to real world Discourse (EmberJS, Glimmer) performance.
We always wondered why Android was so crazy ridiculously slow at our real world JS vs. iOS starting in late 2013 onward.. getting worse and worse over 2014 and 2015.. and "gee, we optimized for the wrong thing aka Octane" was a big part of that.
JavaScriptCore (WebKit's JS engine) also optimized for Octane. But we additionally optimized for Speedometer, Sunspider (the not totally broken subset that made it into Jetstream) and JSBench. While Octane isn't the single answer to all JS performance measurement, using it in combination with better things seems better than not using it. To go back to your example, iOS both has way better real-world perf and way better Octane results than Android devices.
BTW benchmarks I'd endorse include MotionMark, Speedometer and Jetstream from http://browserbench.org/ as well as JSBench http://plg.uwaterloo.ca/~dynjs/jsbench/
These are all good at testing different aspects of browser performance including relevant testing of the JS engine.