What does a psycannon bring to the table?
A psycannon has two firing modes, assault 2 and heavy 4. At both, the cannon fires at S7. Essentially, on a regular power armor marine, you have a mobile autocannon. The shennanigans really start when you drop this baby into heavy mode. Alongside the Heavy 4 comes rending. That means if you have a terminator carrying a psycannon or if you have a power armor model that is stationary firing the cannon, it becomes a behemoth of troop and, yes, armor killing potential.
The fact that terminator armor bestows the "relentless" rule means that terminator wearing models can move in their movement phase and still fire the psycannon in its heavy 4 rending mode. If you look back at my small elite force that I army listed out a few days ago (Linky), you can see that I tried to make use of this as much as possible.
Another marvelous way to run psycannons in a GK army is to steal a little tactic from our friends the Sternguard vets who double up heavy weapons in rhinos. By putting a ten man power armor squad of any kind in a rhino, you can take 2, if not more, psycannons in that rhino and set up a midfield bunker shooting 8 shots at S7 with rending when stationary. On the move, it can still fire 4 S7 shots! Amazing!
What the psycannon offers for the GK codex is unparalleled mobility while still retaining a high number of high strength shots. This definitely doesn't push them up ahead of IG in terms of shooting potential, but it certainly makes them far more competitive, light years in fact, than they were previously. I would gladly trade the extra 6-12" range for the capabilities that the psycannon now has at 24". That said, I think this gun alone is going to make Grey Knights scarier. It also makes running a pure Grey Knight army viable and competitive.
So, what your thoughts? Do you think psycannons are that deadly? Am I just dreaming? I am anxious to hear what other people think. On paper and in games that I have played, the gun is just monstrous.