Dan has just posted a method of overclocking the Dreamcast that allows for a 10% gain in speed by changing the 33.333Mhz clock to 36.7Mhz. While there have been other mods available in the past that can overclock even higher, this is a much easier mod to perform: Simply remove the three resistors in red shown above, then add 10K 0603 resistors to the two locations marked in blue: http://dansprojects.com/dc_overclock.html
Overclocking like this should improve the overall performance of the system, reducing slowdowns and increasing framerates. In most cases, your games should play at the same speed, unlike overclocking something like Star Fox, where the faster the clock is set, the faster the game will play. Also, this mod is compatible with the DCHDMI, as it uses the video clock for timing.
As with all overclocking, you run the risk of wearing out your console faster, as well as creating heat issues. While overclocking 10% is certainly safer than the previous 20% overclock, I’d suggest upgrading the fan. Since you’re already taking apart your Dreamcast, you might want to look into some more of the preventative maintenance, as well as enhancements available! Check out the videos below for more info: