Today I picked up the new guard 'dex. I had read it quite a few times at my LHS but getting it home I really had a chance to read all the special rules. I just realised how damn good sanctioned psykers are now.
The battle psykers have 2 powers, 1 makes a large blast (str equal to amount of models in unit) and the other weakens enemy ldr. Both are range 36".
The primaris psyker can either do 2d6 str 6 ap 5 hits, or obscur the unit the psyker is with (enemies must pass a ld check or they wont shoot at all).
I played a game with my dad using three full units of battle psykers (thats 10-man squads) and a primaris psyker (a hq choice). I used a solid block of infantry to drain all the enemy fire, than I used my 3 griffons, valkyrie and psykers to dish out 8 large blasts a turn, than I started usin the other psyker power, that drops the target unit's ld by the amount of psykers in the squad. Combining that with the griffons and rocket pods, I managed to flee enemy units off the board for losing 3 guys (and the units fleeing were tooled up ig vets). All this time I had a 20 man infantry mob and a 35-man conscript mob sinking enemy fire. In the end I called the second wave with the conscripts (giving my dad a kill point) and lost 1 psyker squad, winning the game 7-2 (killpoints).