I happen to have some data like what you're asking about for 1/1/16 - 12/31/16
Your comment on "faves in last start" is true with Impact values near the top of factor list.
Code:
Impact
Starts Win% Value ROI Factor
29728 44.22% 3.446 0.875 fave today
12364 24.58% 1.915 0.769 fave in last and won
13219 20.70% 1.613 0.739 rail start 1/2 mile
15356 20.40% 1.589 0.782 fave in last and beat
28763 19.85% 1.547 0.757 won last race
3167 19.23% 1.498 0.828 claimed in last
27547 14.57% 1.135 0.777 different track last time
9043 14.44% 1.125 0.8 rail start 5/8
104816 13.33% 1.039 0.716 tracksize1/2
237879 12.84% 1 0.744 all starters
74810 12.60% 0.982 0.735 tracksize5/8
21994 12.45% 0.97 0.822 tracksize1
36259 12.10% 0.943 0.797 tracksize7/8
2518 11.68% 0.91 0.819 rail start 1
4074 11.19% 0.872 0.688 rail start 7/8
26910 10.09% 0.786 0.699 driver is trainer
209545 9.17% 0.714 0.725 ML>2.9
Best in category in race
23133 24.10% 0.84 My Speed
23133 28.90% 0.81 TM Speed
23133 22.10% 0.77 Yr Earnings$
23133 22.00% 0.76 TM Class
23133 20.40% 0.75 Top UDR Driver
23133 19.10% 0.75 Top W% Trainer
23133 17.20% 0.75 Early Speed
23133 19.30% 0.74 2Yr Win%
23133 19.60% 0.71 Fastest FT
23133 16.30% 0.70 Fastest 4QT
