Just read this on http://www.vg247.com/2013/05/10/wii-u-latest-system-update-has-increased-cpu-gpu-speed-rumour/nintendolife, which also points out no credible source. I'm no tech expert and don't know if this is even possible. What do you guys think?
Edit: Maybe this link will work better: http://www.nintendolife.com/news/2013/05/rumour_the_recent_wii_u_system_update_has_boosted_clock_speeds