I found in last years snow (loads of snow) that my Captiva did most of the running about (in the snow) using just the 2WD. It has a lot of torque and the snow didnt bother it at all.....
Saying that, when the 4WD cut in, it became another animal completly, and nothing bothered it at all.
I should add that only once I needed the 4WD, but I was really glad it was there, as without it, I reckon my car would have been stuck at the bottom of the hill with other 2WDs for 2 weeks, as they where. But most times the 4WD only cut in because I acted like a kid and put my foot down to spin the front wheels.
Of course the other benefit of the 4WD models is the 7 seats. I dont use the 7 seats often, but on the occasion when 5 seats is just not enough (like a day out with the family and parents) the rear 7 seats have been worth their weight in gold. Should also add, they are "real" seats. I, and a mate, both of us not small, have travelled in the very back from a rugby game, when my wife picked us up. Also had 3 mates in the middle row (back seats) and a mate in the front who is 6' 7". The journey was nearly an hour long and not uncomfortable. The very rear seats leg room isnt great, but to be honest, my wifes car is a Corsa, and I reckon the space in the very rear of the Captiva is no different to the Corsa.
As Binginaw has said. It is really down to budget. Dont think you will be disapointed with the 2WD Captiva, but there are real bargains out there with the new model on the way, if you are prepared to look (and maybe travel).