I'm currently running mine at 1.7ghz no sweat and I see there's now one that pushes to 1.8ghz. Check out the xda skyrocket android development forum for the appropriate kernel and instructions
hint: [KERNEL] AT&T/Rogers dag .42 1.83GHzOC/UV/init.d/BFQ/BLN/FUSE/adb root/optimized
**At YOUR OWN RISK**
*I am not responsible for any device damage or malfunctions*