Any idea if the Sabertooth can be run at 18volts, using 24 volt or greater electro caps?
If you check that all your parts can handle 18 volts or preferably more, then yes you can! If it actually sounds good at 18v is another question. I don't hear many people feeding fuzz pedals more than 9v. I hear more stories about fuzz pedals sounding better with dying batteries / less than 9 volts.
speaking of dying batteries. this is a super simple build if you want to mess around with that kind of stuff:
http://beavisaudio.com/Projects/DBS/ (http://beavisaudio.com/Projects/DBS/)
very fun little guy to have on the bench.
I say "never say never" most of the time, but I don't see any benefit in doing this one at 18v. But, if you do find something unique or cool about it, please let us know!
I'm also curious how it would sound at 7.5 - 8v.
The reason people typically run pedals at higher voltage is for greater headroom. In other words, the voltage swing of the signal can be higher before it reaches the supply voltage and starts to distort.
If you're building a distortion or fuzz, (depending on the design of the circuit) you're taking advantage of the fact that voltage swing can never exceed supply, and that's what's changing the waveform of the signal.
So running distortion or fuzz circuits at higher voltage may give you some cruddy results, but again it depends on the circuit. (off the top of my head, some designs that use clipping diodes may actually distort more since they rely on the voltage drop across a diode to shave off the top of a sine wave. this assumes that more supply voltage means more gain, which isn't always true for many circuits).
conversely, running fuzz and distortion pedals at lower voltage often makes them crazy distorted by the same explanation above.