You know the biggest and baddest jack is the cryxian deathjack right??
For an army of jacks you have the right idea. I just want to point out that Karchev plays very differently then other casters because he is a man in the machine. You might want to start with butcher or vlad, because they offer a bit more in 25 pts I believe.
Things to watch out for are fast jacks from the opponent. A few big hits from the right jacks will take out most of your systems.
If you believe in the list then try them, but I would say try it with another caster for the low points game, then "upgrade" the caster for 25 or 35 points.