King tiger.
The speed advantage is over rated. Tank victories always come down to acuracy, firepower, and lastly Armor.
The bigger gun on the Tiger gives it a better chance to shoot through a panther at distance. It's thinker armor makes it more likely to survive a panther hit at distance. at 3k a K Tiger could survive 3[?] hits from a Panther. How many hits could a Panther Survive at 3K from a KT? Fire rate is similar? I think so. That one or two more hits that KT can take over his opponent makes him a winner.
I'm not so sure to rule out Speed, there's a reason I ONLY take the Panther/T34/85 is for the burst of speed, granted Its not going to get you out of trouble as an M3 or m8 will, however taking the time to aim and fire on a moving target thats feet away from a hill can make a difference.
One more thing to note, Its very rare to score successful hits on a moving tank at 3k. That being said depends on the experience up to this point, some days I can fire 20 rounds at 3k and not hit, other days I can fire 20 and guess hit 15 outa those 20. It depends on the situation, remember Aces high rarely has any clear 3k shots.