We now have a successfully compiled kernel for the Captivate that overclocks the phone to 1.2 GHz. The link is coming soon. Also, many are complaining about garbled audio on custom kernels, even compiling directly from source. Either way, that is now fixed:
GOT IT! Sounds perfect again! Just download the Vibrant source and copy the ENTIRE sound/soc/codecs folder over to the Captivate source. Like I said before, they are almost identical for the most part, so I looked and saw the A1026 files were in the Vibrant source, among other missing files, turned on A1026 in the .config and copied the codecs folder and it sounds good as new again! I'm already late to go meet some friends messing with this, so try it out NukaCola and see if it works for you. I'll test the rest of the audio as I go, but this is good so far. When I get back I'm going to ext4 enable my kernel, OC'd to 1.2 GHz and see if I can hit a 2K quadrant score, haha.
The i9000 folks have successfully created a 1.2 GHz standard voltage overclock. Is anyone over here interested in helping to port it over to the Captivate? I have no experience in kernels, but I'd love to learn and do my best to help out. Here is the link: http://forum.xda-developers.com/showthread.php?t=743782 . Also, the few of us with Linux or OS X would love to see an option for flashing from recovery. Just let me know if anyone is interested, and thanks in advance.