From another forum:
http://www.focusfanatics.com/forum/mk3-focus/664434-upgrading-my-st3-lights-35w-hid.html
I sourced parts from a 2014 Jaguar XF and swapped the 25w components with the 35w components. I would gauge the improvement at around 30% in brightness and throw. I managed to source all the parts as a package for $120 shipped.
If you're looking for additional light output, this works well and is a super easy swap.
http://www.focusfanatics.com/forum/mk3-focus/664434-upgrading-my-st3-lights-35w-hid.html
I sourced parts from a 2014 Jaguar XF and swapped the 25w components with the 35w components. I would gauge the improvement at around 30% in brightness and throw. I managed to source all the parts as a package for $120 shipped.
If you're looking for additional light output, this works well and is a super easy swap.