EHLO

Yeah, the 5.2L V10's compression ratio is a high 12.5:1.
I'm assuming the denser winter air keeps timing in an acceptable range so it's not noticeable.
The site pure-gas.org keeps track of ethanol free gas stations.

Greg5OH

dont know if OP purchased an S8 yet, but we put 8k miles on ours in the last 2 months and LOVE it. bought it at 72, currently at 80k miles.
dealer did the brakes before we bought it, but still cheap to do yourself, about $400 for pads and 4 quality rotors. I did front upper control arm bushings, now have to see about the locked open rear ebrake, either stuck or just dead. I wouldnt callthat a reliability thing, its an external common part.
Reliability to me means engine, transmission and electronics which the car needs to function correctly. Knock on wood, all good for now.
Yes, if you dont do the work yourself it is expensive. Heck even if I have to change timing chains I will still do it at home at my shop, but from the mileage I have seen of a few 07s for sale, these are solidly built cars.

EHLO

The low speed stumble was because one of the header flex pipes was leaking, drawing air in under deceleration, which confused the post Catalyst O2 sensor.
Aluminum muffler wrap fixed that.
Here's the code (other side is P3298);
19755 - Catalyst System; Bank 4: Efficiency Below Threshold
P3299 - 001 - Upper Limit Exceeded

dvs_dave

I recently had both flex pipes on my 4.2 replaced as they were leaking. Aside from it being quieter, there was a slight engine shudder at 1800rpm that also went away. I didn't have any codes though.