Having had Opel Zafiras's before buying the Ford, I was in the same sort of position as you are now. I am very happy with my decision and have enjoyed the better handling that the GCM over the Zafira. I am also pleased that I went for the 2.0 TDCI over the 1.6 too.
I don't know what you had before, but when loaded up with seven people or a decent load the 2.0 has, to me, the edge. That will depend on what you were used to before though and what your driving conditions are too. I had a 2.2 petrol before. I tend to be a cruiser more often than not though I've been doing quite a lot of town driving recently, and have been getting with the last three tanks; 6.08, 6.12, 6.49 per 100km which equates to 46.19, 46.44 and 43.49mpg which I'm happy with. I like the interior, though the centre console does attract the dust! I love the Sony sound system and combined with a 32Gb memory stick beats a lot of top luxury models for sound and storage.
One thing I did though, is not added the two rear seats. I spec'd mine as a five seater. That means I have a much bigger boot than a GCM and also bigger than the CM, which is useful for me.
Grand C-Max 2.0TDCI Titanium Colorado Red
Tinted windows - bi-xenon/washers - 17\" Wheels
Sony Gps SD Hands free - reversing camera - parking sensors - key free