Hi Party,
You a pretty right with the ROI, it is basicly the same but the SR is different.
Stats show more favs get up in races 1-4 than 5-8 but the the ROI is similar.

Stats show that...
Race No.1 has the highest SR 36% & lowest av. div & a LOT.

Race No.8 has the lowest SR at 24% but has the highest average div a manages to nearly break even.

So if one were targeting a race for favs. race 8 offers the best chance of breaking even, along with longer runs of outs.

If one wishes for the highest SR regardless of price.
Target race No.1 then 2,3,4

Cheers.

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Cheers.