It doesn't really matter, because x86 processors inside are almost similar to modern ARM processors, the instructions that most programs use are more or less the same, and more complex "legacy" instructions are just emulated by splitting them into simpler instructions inside the CPU.
To me people that say that x86 is slow etc. never used an x86 processor with anything other than Windows. Yes, Windows is shit and laptops that run Windows are for the same reason shit. I get it. But on an x86 system you can run other OS, and, for example, a Linux distro with well tweaked power consumption parameters can get you even 3 days of battery life, or even more.
The point is that Windows keeps almost always the CPU above the minimum frequency, because it's full of useless background services, because programs are not well optimized for the hardware (to maximize backward compatibility they don't compile target x86_64 v3 for example and thus don't leverage on features and instructions available on new CPU or fall in the emulation case I've mentioned initially), and other reasons.
With a Linux distro you can keep the CPU at 600Mhz while web browsing, you can even turn off cores that you don't need, and the battery with this configuration surely lasts ages (at that point it becomes more predominant the consumption of other peripherals such as the display).