Not sure this will help you but the way i use to rate races was like this, each class from my perceived lowest to highest was give a number like this.
G1 3
GROUP1 3
GP1 3
G2 5
GROUP2 5
GP2 5
GP2 5
G3 7
GROUP3 7
GP3 7
Listed 9
LR 9
Quality 10
Open 12
HCP 12
HANDICAP 12
100 12
96 13
95 13
94 13
93 13
92 13
91 13
90 13
Class 6 13
Cl6 13
C6 13
3MW 15
2MW 15
WELTER 16
Flying 16
90 18
89 18
88 18
87 18
86 18
85 18
1MW 18
0MW 18
One Metro Win 18
No Metro Wins 18
Set Weights plus Penalties 20
Class 5 21
Cl5 21
C5 21
84 21
83 21
82 21
81 21
80 21
79 21
78 24
77 24
76 24
75 24
74 24
73 24
72 24
71 24
Class 4 25
Cl4 25
C4 25
Class 3 27
Cl3 27
C3 27
70 30
69 30
68 30
67 30
66 30
65 30
64 32
63 32
62 32
61 32
60 32
59 32
Class 2 34
Cl2 34
C2 34
Class 1 36
Cl1 36
C1 36
58 39
57 39
56 39
55 39
54 39
53 39
52 39
51 39
50 39
MAIDEN 42
MDN 42

I also included these special penalties.

3Y 5
3YO 5
3F 5
2Y 8
2YO 8
2F 8
FM 3
MARES 3
F&M 3
C&G 3
CG&E 3
WFA -2

I also used this race value component.
IF(AU3="","",IF(AU3<10000,14,IF(AU3<25000,12,IF(AU3<40000,10,IF(AU3<70000,6,0)))))

So if the last race was 50k Open it would get a score of 18
If todays race was a 75k Open the score would be 12
I would calculate 18-12 to get 6, the lower the better

__________________
One Drive

"If the corporates are treating you poorly , just go elsewhere."
"If they need you , they will soon find out."
"If you need them , you will soon find out." --moeee
_______________________________________________