will panther gun defeat frontal armor of KT?
Not the turret or the glacis plate.
It could defeat the lower nose armor at 1000yds or so (assuming he isn't shooting 'down' at it, and therby increasing the slope for that particular section of armor.)
Kingtiger had 180mm turret armor, ~180mm armor on the glacis plate, and ~135mm on the lower nose.
Only 5 tanks will be physicly capable of killint it from the front, assuming a level hit "Tiger, Panther, firefly (lower nose), T-34/85 and the Tiger II.
IMO, KT is gonna mop the floor with the panther. Yeah the panther is faster, but its not fast enough to swing around the sides and make a kill before the KT backs up behind cover and turns to face the panther. M3 probably has a better chance against the KT than the panther, assuming a flanking manuver.