So what's the word, boss?
The first year model of the S80's (MY1999) had a fair amount of problems, and so in general I think people try to go for a MY2001 or later model as they'd gotten all the bugs worked out. MY2000 is sortof in the gray area. As for the T6, I wouldn't be too worried about the twin turbos. Volvo's been working with turbos for a long time and I'm confident they know how to put a turbo or two on an engine and still be plenty durable. They provide a nice amount of power in my mother's XC90 T6. It's bound to be pretty nice in a sedan. And as mentioned before, go over to
www.swedespeed.com and see what people over there say.
As an owner of a new S60, I love my car. I love Volvo's design both inside and out. I'm not at all worried about the life of the turbo in mine. I plan on taking care of it and have faith that it'll take care of me for many years to come.
I will be jealous of your rear-seat legroom, though...