i'm not thoroughly convinced that USB overclocking will make that much of a difference for devices like gamepads with the Pelican.
As far as damage to your other connected devices, i haven't found a single reported incident, though devices DO seem to stop working high polling speed for Hard Drives is a resource hog, and detremental to its speed. There is also the importance of what kind of USB controller chip you have, and if it will play nice with your connected devices. There is also a document that mentions that each USB device comes with it's own Polling Interval value, that was primarily introduced when USB spec upgraded to 1.1.
Anyway, if you can read it, it's here:
http://www.lvr.com/usbfaq.htmit could be, that the Pelican was originally designed for Guitar Hero, that it was manufactured with a high default polling speed, we won't know unless we get a readout. Though for you other people with other ps2-usb converters WITH lag, maybe this tweak can help you.