Pretty much what you're reading here is pretty accurate. You can really cruise on sections of the PCT, especially along the JMT highway. You know the AT, its boulder to root to boulder to rock to stump....etc. If you can pull 20 mile days on the northeast AT, you should be able to at least equal this on the JMT...if not exceed it by 10-20%.
The one X-Factor with the JMT for you is going to be altitude. It might get you, it might not. Are you hiking N-S from Happy Isles to Whitney? If so, and assuming you're coming straight from the east coast, you'll be at 7-8K elevation fairly quickly. If you're not a purist, skip the climb up out of Yosemite Valley and start Tuolumne. That way you can bum around Yosemite on the first day, do the tourist thing and gawk at the rocks, then spend the night at Tuolumne to 'acclimatize' of sorts.
Due to altitude its a good contingency to plan for a start day of 10-15 miles. Be prepared to feel a bit out of sorts appetite-wise over the first bit...possibly until you're out of Yosemite. Make sure you chug the water over those first few days...good idea to start that a few days before the hike, actually. You'll also sleep a little colder over the first night or so, but probably won't be an issue if you hike July-August, though the heat and bugs might.
Another potential spoiler- UV radiation. It's much more intense when you're exposed above treeline at 10K than it is out here. Don't let your fiancee try to get that rad Cali tan on the hike, like my wife did! Pack sunscreen and cover up the arms/head/neck for sure.
If you're used to hiking the green tunnel like the rest of us right-coasters, you're in for a real treat on the JMT. You guys will be grinning for 14 days straight or your money back.