So if someone was going to do a PK shifter in the ranks of 30-35 and you could pick your forms, what would you take to be the most pk effective.

I think Boar and Sand Lizard would be rockin. You have general dodgyness/regen/concealment with the lizard and the Boar has some lag (charge) and direct damage (charge/gore). I think either scion (for the hp and tracking on nightwalker) or outlander(concealment/beast call or ignite) would be the cabals to go.

Has anyone ever taken a serious stab at being a mid or low rank shifter killer and had a measure of success?

Crag soarer + Boar would be nice.

Copperhead + Boar would also be nice.

Sand Lizard + Beetle would be nice.

I think if you got a reasonable hp set + some aura wands, you could do pretty good as a mid 30s shifter. Something like 30-10 wouldn't be unreasonable.

first time around I got two snow forms, one of which was ok for pk'ing fire giants with. Second time around I got two of the weakest off/off forms at that level. So I quit trying.

Boar/lizard would be ideal, imo. Or ocelot matched with snow badger/cobra/boar.