Run fast enough and what do all those jumper wires do?
I wouldn't think the external bus would run anywhere near the speed of the processor at the higher speeds. For example, it seems you can only get 22Mhz out of the Raspberry Pi despite the relatively high (non-overclocked) clock speed of 700Mhz. I would expect the 1-1.5Ghz processors I was talking about would have bus speeds around that too. Instead, I am mostly interested in having such processors available for their relatively better computing power.
http://codeandlife.com/2012/07/03/benchmarking-raspberry-pi-gpio-speed/