storm,
My humble opinion. Top 10 horses in the 90's/2000's in no particular order are Better Loosen Up, Octagonal, Saintly, Vo Rogue, Super Impose, Let's Elope, Might And Power, Sunline, Rough Habit, Tie The Knot.
That's 3 Melbourne, 4 Sydney, 2 NZ and 1 Qld.
Melbourne horse has not won the Cox Plate since Super in '92. Often only 2 or 3 get a run.
I think Melbourne racing has superior depth to Sydney racing but at the top of the heap Sydney horses win a disproportionate number of Group One's.
P.S. Probably the best horse out of Melbourne in the last 3 seasons, Testa Rossa has won less G1's in Sydney than Sydney's best Tie The Knot has in Melbourne.