Well if carrying 5 tall adults really is a big issue, I would say the Espace is the way to go. But if the car has to carry 5 adults from time to time but not that many, maybe a sedan is more interesting.
I've driven all three sedan contenders: the MY01 S80 (pre facelift model), the MY02 9-5, and the MY00 607. All with petrol engines, but I've experience with Volvo's 2.4D and the GM (Saabs) 2.2 TiD.
As for the 607, I've only driven it for about half an hour. And we've only tested it with 4 adults in the car. So I can't tell you that much. The boot is really big, it has a nice ride: comfortable but no dull handling. Interior build quality is mediocre (it also changes it bit from car to car) and sometimes reliability can be an issue (it also depends from car to car).
And now for the Volvo S80 and Saab 9-5. We own a Saab 9-5 and before purchasing it we did some extended testing with the 9-5 and the S80 (pre facelift model). So I do know quite a lot about those two cars.
Both are big cars with a big boot. We tested both driving with 5 adults in the car. The person sitting in the middle in the back seat of course has not that many comfort (an Espace will be better for this), but it won't give any hernia issues
We concluded the back seat of the 9-5 was a tiny bit more comfortable than in the S80. But both Saab and Volvo had really good (front) seats, certainly of you opt for the sport seats. We preferred the sport seats of the Saab above the ones of the Volvo, but only with a really small margin.
Build quality of the Volvo is better than the Saab. The used plastics are better quality and everything fits more neatly into each other. I also think the Volvo is a bit more reliable (but I can't really be sure about that).
Ride and handling. The standard S80 suspension is really set for comfort. The problem is the handling is a bit vague and dull. We were looking for a car with comfort but also some crispy handling. We actually have never tested a 9-5 in standard setup, we've only driven the Vector and Aero versions, which are a bit lowered and harder damped. We did like them because of the nice mix between comfort and some more dynamic handling (but don't expect handling like a sportscar or a M5). The standard S80 setup has more comfort, but compared with the S80 with 'sport' chassis (the 4C chassis didn’t existed in those days), the 9-5 Vector and Aero are better. We thought that they gave us just a bit more comfort (maybe other persons think it's the other way around) and the handling is far better. Even with the 'sport' chassis the S80 had troubles coping with loads of power and torque (we tested the T6, the less powerful versions prolly won't have those problems). So that's why we liked the 9-5's ride and handling over the S80's. But bare in mind we were judging the sportier chassis setups and not the standard ones.
The engines. I would strongly suggest not to opt for the 2.2 TiD. It really is an old diesel engine: it makes a lot of noise and vibrates quite a lot. Some sound proofing can help but the main problem still exists. As for the Volvo I would suggest the D5 over the 2.4D. Those extra horsies just make driving it a lot more fun and relaxing.
I hope this info helped a bit. If you have further questions just ask.