Lots of conflicting measurements but from the AFL site:
MCG
Capacity: Approx 100,000
Ground dimensions: 160m x 141m
Metricon Stadium
Capacity: 25,000
Ground dimensions: 160m x 134m
I wouldn't think 7m in width overall is significant in the big picture of ball movement.
A couple of others just for interests sake:
The Gabba
Capacity: 42,000
Ground dimensions: 156m x 138m
Patersons Stadium
Capacity: 43,082
Ground dimensions: 175.6m x 122.4m
SCG
Capacity: 45,500
Ground dimensions: 149m x 136m
ANZ Stadium
Capacity: 81,500
Ground dimensions: 159.5m x 128.8m
Etihad Stadium
Capacity: 53,355
Ground dimensions: 159.5m x 128.8m
Simonds Stadium
Capacity: 28,300
Ground dimensions: 170m x 115m