Sounds like fun.
What are the approximate dates of this trip? If in June, or even the first half of July, the snowpack may heavily influence your options in some locations.
You say you're in great shape. Are you in great HILL shape? A 17-mile day in the High Sierra is going to be dramatically more difficult than a 17-mile day in Oregon. You might be talking 5000+ feet of climbing per day, and the same amount of descending, with a pack, moving very slowly because you're at 11k or 12k or higher and are not acclimated. PCT'ers racking up 20-25 mile days in southern California usually slow down to 15 miles/day once they hit the Whitney area. It's just very taxing. If in the High Sierra you could maybe aim for, say, ~12-14 miles/day instead of trying to make 100 miles in 6 days.
Most people I talk to who've done the whole PCT (I've only done certain sections) preferred either the High Sierra between Whitney and Yosemite, or parts of Washington State, especially the trek through the North Cascades (north-central Washington). The WA section from Snoqualmie Pass to Stevens Pass is probably around 100 miles, and I can highly recommend that one. Someone also mentioned Bishop Pass to Mt. Whitney in CA, and that's also about as good as it gets (although it is also very high/vertical/difficult, so check the mileage to make sure that doesn't create 18-mile days).