Not an exact comparison really, but I switch my 19" summer wheels for 18" snow tires. I imagine much of it is compound & taller sidewalls, but the ride is so much better on 18's when PASM is on firm that it is really quite a nicer car for general driving.
Part of this too might be the switch time - usually around now. I took the car out on dry pavement at 6:30 this morning (29 F) on the original PZeros, and they were hard and slippery. So it could just be that they ARE harder flexing as it gets cold, and when I switch to the 18's on Thanksgiving weekend, the change is that much more noticeable. Maybe in July (or Texas
) it would be less so....
Anyway, I got the car in 2009 and drove it the 1,200 miles from Miami in 1.5 days, and it was fine for a long trip even on the 19's in the summer. But it was new, and I was excited, and coming from a sport-shocked 1987 Targa. Living with it everyday for 1.5 years now, it could use softer tires for the day to day driving. At least for my regular driving style, and the fact that I don't track or autocross....
I understand the PASM worries, but I've found that it is nice to have a softer setting for around town. At highways speeds, I usually put it to firm to stop a slight floaty feeling. The firm setting is just like my 87 sport shocks, but the seats in the 997 are more firm than those in the 87, and that sometimes makes it feel too firm overall. I liked the ride in the 1987 firm car with the slightly softer seats better. Obviously, YMMV, but you might want to take a look at all the seat options as your trip is a kind of Grand Tour. That said, long-day comfort is great in the 997, as is the lumbar adjustability, etc.
I suppose it isn't really the sitting in the harder seats that is the problem, but the getting in them: I had the 87 for 10 years, and after 1.5 years with this one, I still sometimes plop down in the seat and hit my back on the side bolster - which is way harder than in the old car.....funny thing is, the headrests in the 997 are way softer, which is nice when you stretch your neck.
FWIW - I have the Bose stereo and it is great - except it is sounds so good that you can actually hear the difference between the radio/CD and a CDR you've burned from iTunes. You always hear stereo folks say MP3's/iTunes doesn't have the range of real CD's - and this seems proof. I travel a bit, and have those Bose noise-cancelling headphones, and can't hear the difference anywhere except in the car....