Here's the thing. Junky is right, you should just use the K4 if you want to roll with the 30mm. One reason is because it's harder to shoot and you might have to go around for another pass. The K regains E a lot better. The other part is the K does not have those bumps on the nose. There it makes the K easier to make a shot, the G14 would use extra E to get kills, thus not making it the best plane for the 30mm.
The G14 is the plane you want to roll when you need to have some solid gun power. I normally use the gondies, unless in the Dueling arena. I like the G14 because it's a litte easier to set up your shots and you can rake planes with bullets in a deflection shot or turning shot. This way, you get the kill on the first pass instead of having to go around again and lose a bunch of E.