An update on results:
METRO TRACKS ONLY
Selections: 41
Winners: 9
Strike Rate: 21.95%
Profit: $1.70 (TAB prices)
POT: 4.15%
Average Dividend $4.74

Last winner:
24/9/03 Eagle Farm MASINDOR $2.90

TOPWEIGHT IN WELTER UPDATE

Rules
Welter races
Back the topweight.

Selections: 43
Winners: 9
Strike Rate: 20.93%
Profit: -$0.30 (TAB prices)
POT: -0.70%
Average Dividend $4.74

Taken a bit of a dive lately as suggested by other posters.
I would like to add additional filters to this, but the small sample size is dangerous.
Will wait until I have at least 100 races before adding any further rules.

Update:

Rules
Welter races
Back the topweight.

Selections: 46
Winners: 9
Strike Rate: 19.57%
Profit: -$3.30 (TAB prices)
POT: -7.17%
Average Dividend $4.74

Taken a steep dive for the worse, so I'm going to add an additional rule which is must have won at the track.

I realise this is retrofitted but the extra rule is logically sound.

Amended Rules
Welter races
Back the topweight
Must have won at the track.

Selections: 5
Winners: 3
Strike Rate: 60.00%
Profit: $2.10 (TAB prices)
POT: 42.00%
Average Dividend $2.37

Interesting to monitor this for a while.