You can definetly OC higher than 2.4.
First of all, give your memory 2.8-2.9v instead of stock- that alone may allow you to keep all your settings as they are with CAS 2.5 and OC to 2.4.
Now, that being said- you can get higher than 2.4 easily probably. Figure out how to use the memory dividers to run the memory at a lower speed than the FSB, and with aggressive timings. For the most part- tight timings are what benefits AMDs the most, as opposed to high speeds.
Let us know any specific questions you may have with BIOS settings.
Also, if you don't have it already, download the "CPU-Z" utility.