The effect of cable problems is sparkles in the picture, or even the picture breaking up. Analog gets lower quality with longer cable length, however the great thing about digital is it's totally immune to this.
However, you get increased errors once the cable gets too long for the receiver to compensate for the length. So everything is fine, and then you add a little more and it falls over.
As an engineer in post, I always used to have a long cable I would add to everything I installed to make sure I was ok, and not on the edge. The last thing I wanted was a problem in the middle of a job! (or middle of the night!)
The SDI spec is generally designed around 300 feet or 300 meters of cable length. I need to check that because I have forgotten if the standard is feet or meters. I am not exactly sure what the Kona can do, however it should handle the length you need without any problems.
The other option is to put the G4 next to the deck, then extend the monitors and keyboard to the suite. This is what we do... all of our avids and kona/decklink stations are in our air conditioned machine room. Gefen makes some great extenders for this. And it keeps the suites nice and quiet =).