Zarboz is a developer who’s released a working custom kernel named the EvilZ Kernel for the rooted HTC EVO 4G LTE, that can overclock the processors to 2.1GHz on some EVOs and still run stable.
Overclocking the processor generally causes the phone to run faster, but eats up more battery life and in some cases actually slows the phone down at certain speeds. It also causes more wear and tear on everything, as the phone runs hotter. (However in two years of overclocking the EVO 4G LTE’s predecessors, I still have yet to blow one up.)
The performance gains by the overclocked kernel show up in Quadrant scores as about a 7-10% increase by going from 1.5GHz to 1.9GHz, so there are some improvements to be had. Most EVOs can overclock to under 2GHz, but if you manage to overclock and lock your EVO up, you may simply have to wait for the battery to completely run out – power+vol-up+vol-down is evidently a kernel-level power-switch, and not a hardware-level one.
The kernel is still in beta candidate stages, so it might not be wickedly stable at the moment. But it probably will be soon enough.
One other interesting tidbit about the development of this kernel is Zarboz created this without having an EVO 4G LTE in his possession. All work has been done blindly, with testers reporting back on what’s going on.