This can be a tricky question.

I feel one needs a min of 3 lots of 150 races.

This will give us a rough picture if the system has any legs or not.

If one batch produces a profit & the other 2 batches brake approx even , you may have a possible system.

I have invented plans based on 3 years stats & in the 4th year , it fails to show a profit - frustrating stuff.

I feel one should try for a consistant 22%+ SR , next ,try & get the best possible price , usually Betfair.

At the end of the day , its the terrible prices one accepts from the TABs that eventually kills most systems off, while trying to recover past losses.

Cheers.

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Cheers.