Keep your 4 cyl!!! You will need it when the S80 is at the dealer for dealer only repairs. The electronics are terrible. The T6 engine isn't that good either, it tends to overheat if you look at it funny.
All "new" engines are interference, that is why the T belt must be changed. And changing isn't that bad.
Have you looked at any S60s with the 5 cylinder? Or any S70s? There is a reason why Volvo dropped the T6 and replaced it with the 3.2 this year. They lost too many long time customers.

Klaus
--
1975 164 w/174,800mi (Sold) 1995 850T w/91,000mi, 1998 V70R w/129,000mi

I can't speak from personal experience yet (I've had a lot of 240s, though), but I've been perusing this forum for a long time and I've gotten the opinion that the S80 is a potential time-bomb.

The engine is an interference type, and I've read posts that have said that even when the prescribed replacement interval for the timing belt and tensioner is adhered to, sometimes the belt goes prematurely due to an unreliable tensioner-- and you know what that means!

Also, the car has lots of electronic modules/microprocessors and microswitches that perform myriad little duties that make the car fun to own (when all is working right) and unhappiness when they don't work. Fact is, the concensus is to be sure to buy the car (if from a dealer) with an extended warranty that includes these electronic dodads, if at all possible.

Finally, in various AWD forums, I've heard of a "throttle-by-wire" electronic module that fails in cars of this model year period. I don't know if it includes the S80, but it certainly includes the V70 and XC70, so check on this risk, too.

Anyway, just peruse the earlier posts within this S80 forum to get a good idea. Best of luck.