She's "well over 6 feet" so she's not going to be just a few inches above, I'd speculate she's about 6' 7", that would be well over but not close to 7ft and it makes her still seem freakishly tall like she is.
Arthur wasn't defeated by Rhaegar in combat, he lost a joust but that's not swordplay. Arthur towers above all in the series as a true knight and exceptional fighter, he'd have saved Rhaegar and slain Robert on the Trident. I'd say it's Arthur, Rhaegar and then Robert in order of best warrior. I don't think because Robert slayed Rhaegar that he was the better warrior, many factors and luck account for victories.
I love the dialogue between Eddard and the Kingsguard at the Tower of Joy;
Spoiler
“I looked for you on the Trident,” Ned said to them.
“We were not there,” Ser Gerold answered.
“Woe to the Usurper if we had been,” said Ser Oswell.
“When King's Landing fell, Ser Jaime slew your king with a golden sword, and I wondered where you were.”
“Far away,” Ser Gerold said, “or Aerys would yet sit the Iron Throne, and our false brother would burn in seven hells.”
“I came down on Storm's End to lift the siege,” Ned told them, "and the Lords Tyrell and Redwyne dipped their banners, and all their knights bent the knee to pledge us fealty. I was certain you would be among them.”
“Our knees do not bend easily,” said Ser Arthur Dayne.
“Ser Willem Darry is fled to Dragonstone, with your queen and Prince Viserys. I thought you might have sailed with him.”
“Ser Willem is a good man and true,” said Ser Oswell.
“But not of the Kingsguard,” Ser Gerold pointed out. “The Kingsguard does not flee.”
“Then or now,” said Ser Arthur. He donned his helm.
“We swore a vow,” explained old Ser Gerold.
Ned’s wraiths moved up beside him, with shadow swords in hand. They were seven against three.
“And now it begins,” said Ser Arthur Dayne, the Sword of the Morning. He unsheathed Dawn and held it with both hands. The blade was pale as milkglass, alive with light.
“No,” Ned said with sadness in his voice. “Now it ends.”
Not enough of Jon and Robb's actual prowess has been shown to say they're as good as Brienne