I'm certainly no expert, but I think the Psimitar only served to focus and channel Cable's own telepathic and telekinetic powers, maybe providing a slight boost in effect (though I believe Cable's powers were reduced a bit at the time).
Since I don't know if the Psimitar was supposed to be constructed of especially strong materials, Incredible to Amazing material strength to represent higher-grade alloys might be a decent idea to make it fairly durable. It would likely be capable of dealing damage as an ordinary spear (I'm pretty sure it was drawn as a spear), so a base of Good Edged Damage might work.
I'd say that it might also provide a boost to telepathic or telekinetic powers focused through it, though the wielder must already possess such powers himself. Say, perhaps a +1cs boost (possibly to a maximum of Amazing to Monstrous rank; not sure where Cable's power levels were supposed to be at the time), and possibly enabling the wielder to channel telepathic or telekinetic powers as energy blasts (mental or force, as appropriate) to a range of maybe 3-4 areas, even if the wielder hasn't developed similar power stunts already.
Just some quick thoughts and ideas. Somebody with more detailed knowledge of Cable and the Psimitar may be able to provide better input.