GPIO MHz Operation, What is OK?

Thank you, that helps when I need to condition input levels. I guess it also gives me a rough estimate of what other devices might handle.

I wish there was an IC or understandable filter to build, something, so if I input a 3.3V signal at 25MHz that has some overshoot/ringing, it would at least condition it enough to be logic compatible.

Here is my current problem I've been working with. Just for the heck of it I drove an LM339 (comparator) IC. Basically, Vref was 1.5V and so the 3.3V signal from the GPIO pin on DE1 board was simply reproduced by the LM339 output (decently at lower frequencies). I was doing this to see the frequency response of some random IC I had on hand... wouldn't even output anything above 1MHz and anything in the upper kHz wasn't clean (100kHz was fine ie).

Here is an application I can give you guys:

I want to drive a Fiber Optic Transmitting Module (TOTX147PL). This device has Vcc of 2.7-3.6V. The input high voltage is 2.1V-Vcc. The low is 0-.9V. So theoretically, I think that this half-way mangled signal could drive this transmitter if I had Vcc at 3.6V...

I have no idea if this type of thing works... but try me out.

What if I drive this 10+MHz signal into this buffer gate: SN74ABT125 at ti.com/lit/ds/scbs182i/scbs182i.pdf , if it is powered by 5V, its high level in is 2V to Vcc.

It would output 3.2V typical, the propagation delay is 4.9ns. Does this mean it can't go any faster than 204MHz (fine for me!)??

So, in my mind, I see this thing as being a very nice line conditioner for me... plus it can be a "buffer" between the world and my FPGA, and probably can handle more current. I could use it for my inputs going back to the GPIO pins as well...

Thoughts please!