I think we can safely exclude 100MHz and 2GHz, but you probably already knew that
500kHz looks pretty unlikely too ...
Does this help (towards the end of the post, under: "Bit toggling"):
It's not talking about Netduino in particular but the .Net Micro Framwork in general. But some good insights ...
"So basically, with a 100 MHz processor, you can usually do around 20 ?s wide pulses using managed code (about 25 kHz)."
Another similar discussion on the TinyCLR forum:
"72 MHz sounds very fast.
But I was surprised that outputting an alternating 0 and 1 via .NET code was so slow!
I got only 10 kHz."
So I am guessing it would be less than 10kHz, if your code runs on the Netduino Go and communicates the command to toggle a pin to the shield base over the go!bus protocol ...Go to the full post