XboxOverclock will allow you to overclock the FSB and NVCLK via software. It uses infromation gained from XBOverclock by WulfyStylez.

See the requirements for nxdk.

git clone https://github.com/GXTX/XboxOverclock
cd XboxOverclock
eval $(../nxdk/bin/activate -s) make -f Makefile.nxdk

Then you'll have the xbe in the bin folder.

Once you boot into the xbe you'll see a prompt. Use the left and right D-Pad to change the wanted FSB frequency, use the up and down D-Pad to change NVCLK frequency.