Just thinking about Gk weapon options, and had a thought about how psilencers could have been good. As it stands, they're effectively useless, for several reasons. For one, Gks already have a ton of str 4 shooting. Secondly, it's a heavy weapon only, making it useless on power armor Gks. Lastly, it's useless against vehicles, and Gk anti-tank is almost exclusively vested in their infantry (meaning psycannons), with the exception of Dreadnoughts.
So to make the psilencer useful, you need to differentiate it from other weapons, but still let it fill a niche that Gks need. What is very rare in the codex is high ap fire. Aside from henchmen and rending psycannons, GKs have virtually no AP3, 2 or 1. Make the psilencer AP2 (and changing it from Heavy 6 to Assault 4), and you now have something that fills a useful niche within the GK codex.
Of course, this is still useless against tanks, which would mean that even after making this useful it still couldn't come close to competing with psycannons. So, let psilencers hurt vehicle. It doesn't have to be as good as psycannons (in fact, it shouldn't), but still do enough damage to matter. I'd say glancing on a 4-5 and penetrating on a 6 would be fair, after an appropriate points increase.
Fluff is easy to deal with, too. Just say that the psychic burst from the psilencer warps reality and scrambles circuitry, thus damaging vehicles and bypassing normal armor.
So with that, we're left with a weapon that brings something unique for the Gks, can hurt vehicles so it isn't automatically ignored in favor of the psycannon, and would probably be around 15pts (keeping in mind that GKs lose their force weapon and storm bolter when they upgrade).
On a side note, Psycannons should be 20pts and Incinerators 10. But whatever.