Honestly, I just like running a knight warden, give him the AA option on his back. Run the assassins with him and flush out with either Grey Knights or Imperial Guard. Again with GK your not going to get a lot of model coverage, and if this is a concern then don't run GK, run IG. With guard you will get a lot of models, but easy to kill troop units unless you armor them up a bit. My favorite way to take IG infantry, give them a auto cannon team and flame thrower inside a chimera. As a point I ALWAYS take a FW variant Hydra (for 5 extra points, you get a model that ignores jink saves...screw you elder...) Then if I have enough points ill either a couple of heavy weapon squads with either las or auto cannons. Put enough AC/LAS shots down range even at BS 3 your going to score some solid hits. Your knight will be something they CANT ignore, you assassins will be something they CANT ignore. Doesn't matter whatever else you take, with those units being a huge focus of theirs, it gives you the ability to move around your other units to do whatever you want with them.
Imperial Knight and Assassin unit is almost 1000 points yes, but at 850ish points still, you can build a solid block. Remember, you have to viable threats that your opponent can not ignore. Everything else while maybe filler, can still be effective. The reason I personally advocate the lower model count Grey Knights, is to add is some warp dice to counter their (elder) shenanigans with their 15-25 warp charge base pool each round.
Anyways, there's my 2 cents worth.
Alternatively, you can just rock a Necron army and capitalize on the 4+ re-animation rolls with a knight in the backfield as a ally (maintain your distance so you don't have to worry about any stupid one eye open rolls) I have tried this, and it is VERY effective. Their STR D weapons don't negate your re-animation rolls, and lets face it, if they are within 24" you will definitely bring their warlock on bike squads down or any other bike squads with sheer volume of shots AND still get your re-animation. Oh..and the backfield knight they have to deal with at same time.
Enjoy..