Considering people are overclocking other ARM processors quite regularly (google around for GP2X overclocking), it should be possible from a hardware standpoint, the kernel/software is a different question, though, not sure if it's easy enough to do via procfs or sysfs, or if the powersave functionality will play nice with a higher clock rate. As for bricking, the risk is always there with almost any overclock. A few lockups are almost certain, but if you go too high for too long it might get permanent