actually. a panther has no definate size, because a panther is not a specific species or breed of cat, its a summerization of all big cats, wich is why when somone talks about a black panther....it could be a lion,tiger,bobcat,cheata whatever.....just all black, hence black panther= panther=big cat

but yeah i agree with Gentar.. i think your heading in the right direction , maybe give him 3 tails, anything crazy like that.....but i dont think you should make the legs thin, ( animals with thin legs are fast and built for speed if this animal is supposed to be for fighting and hunting the legs shouldnt be to thin nor to bulky " cats have thin legs and are very fast, large breeds of dogs have huge legs and are powerfull ) maybe try to come up with something sort of in the middle. i can also see the difrences in the animals parts how some are cat-like others dog-like and then the skull is more like a arctic-fox.. all in all nice art .and no dont pay attention to Robinmagus apparently he dont have any wolvs in his area of the world because that looks nothing like a wolf muzzle is to short, legs arent long nuff, well unless its a wolf pup then it does kinda look the same.
about the second set. it looks like his head is deformed hehe ...but ewww take out the spikes lol