Today I've released a new app for the HD2 to control the CPU speed of the device. You can scale the speed anywhere between 128MHz and 998MHz and lock it by disabling the autoscaling feature that HTC put in. Having the CPU at 998MHz all the time (as opposed to the 768MHz default idle speed), you don't notice the battery increase. I didn't at least.
I've also ported some of the code from the Nexus One linux kernel to allow overclocking. Unfortunately it's not possible (or I haven't found a way yet) to increase core voltage, so you can't overclock too far. You should be fine overclocking to 1.1ghz. Overclocking to 1.2ghz is tricky already and I've never been able to clock it at 1.228ghz or higher without it instantly locking up.
Also one other major limitation is that overclocking currently only works on AC power, as on battery the phone somehow enforces the cpu speed at 998mhz (or more specifically, last used performance level) every 500 milliseconds. I'm still trying to figure out how to fix this. :-)
Head over to the thread on XDA for more details.
I've also ported some of the code from the Nexus One linux kernel to allow overclocking. Unfortunately it's not possible (or I haven't found a way yet) to increase core voltage, so you can't overclock too far. You should be fine overclocking to 1.1ghz. Overclocking to 1.2ghz is tricky already and I've never been able to clock it at 1.228ghz or higher without it instantly locking up.
Also one other major limitation is that overclocking currently only works on AC power, as on battery the phone somehow enforces the cpu speed at 998mhz (or more specifically, last used performance level) every 500 milliseconds. I'm still trying to figure out how to fix this. :-)
Head over to the thread on XDA for more details.