Hammer, I'm confused by your maths... from 2.4 to 3.06 is a 27.5% increase in processor speed... but that aside, my recomendation would also be a decent upgrade. I recently went from 2.4 to 3.2 (I have an 875 board), and the performance increase for my DAW was noticeable, projects with lots of plugins that were previously sitting at very high CPU utilisation, to the point that playback would stop, are now working a treat.
Anyway, There are additional major performance benefits to be gained from;
Faster Front Side Bus (data in and out of the CPU)
Faster RAM Clock
Dual Channel RAM architecture
The big question at the moment for building a new DAW seems to be chipset related... do you go to 915/925/945 with PCIe and a limited number of "legacy" PCI slots, or stick with 875 (which I chose to do eventually), for the number of available PCI slots and known chipsets, which are known to work with existing audio hardware. 915/925/945 boards will also have a limited number of IDE (PATA) connectors, having transitioned to SATA as the primary interface for HDDs.
Personally I would (and have) move to Intel SATA RAID0 anyway, if you're working with lots of tracks you need fast HDD access...
I'm wondering how long before we start seeing PCIe pro-audio interfaces?...
Just my 2c, do with it as you please