I was under the impression that Tegra 3's cores were synchronously clocked. nVidia at least seemed to be arguing in favor of this. If this is true then you'd be a lot more conservative about turning on those cores.
All 4 cores run at the same clock, yes. However, when CPU utilization is low -- and the OS schedules it in batches -- then the clock root can be opportunistically shut off. For most mobile CPU's, this requires a few cycles (C1 state in x86 world). This can happen automatically for a WFI/WFE instruction that typically is used when a thread goes to sleep.
It can optionally be used for when there is a (in the case of mobile SoC's) very long latency memory reads and the pipeline is backed up waiting for that load.
This effectively accomplishes much of the same advantages as downclocking. Though obviously, all else being equal, the higher-clocked CPU will still consume more power. Just not as much as you'd think.
And that's the thing I have never understood in mobile phone design. Why would you want to run your software on JIT instead of running native optimized code? Battery sizes are limited, processing capacity is limited and memory bus is limited (doubles take 8 bytes each). Why would you want to waste resources on a platform like this?
Android wasn't created with such a specific aim in mind. Remember that this was in the days of Palm and PDA's. Most of them actually ran Java ME. It made development easy -- this was before the age of app stores -- and the choice of hardware flexible.
It wasn't until iOS that UI "smoothness" was even a factor in most manufacturer's minds. Android originally wasn't even supposed to be touch-based.
While it is a perception thing, I have to wonder how important absolute stutter-free is. I've played around with the One S and there is nothing about the UI that I find lacking in terms of use. Yes, you can push it to the point where the scroll list may skip a frame but I think we've gotten to the point where it's not really a hinderence to usability.
As for efficiency and battery life, the meager processing power required for most applications -- even with the JIT -- is absolutely dwarfed by the amount consumed by the screen, wifi, gps and cell radios.