When I do weight based ratings I use either ozeform ratigs or the ones on the tamanian tote site, both are quite good. Obviously which run you choose as your base rating will make or break you. I was comparing both ratings for several horses the other day and while there is a direct correlation between both, there does appear to be some differences for some ratings. For example a runners ratings might be something like this for its last five starts:

Ozeform Tasmanian tote

54 580
52 560
49 525
55 610
46 415

As you can see the last rating is the lowest in both but the proportioning is different compared to the others. Any coments welcome>