shaun i would be looking at horses going up in wt rather than the reverse.
low weighted horses have an appalling record.
i.e.-50=0.1pc of runs 0.1 pc of wins.
50.5-51.5=1.4 pc of runs =0.7 pc of wins.
52-53 =34.8 pc of runs =21.3 pc of wins.
53.5-54.5 =27.2 pc of runs =27.3 pc of wins.
55 -56 =21.7 pc of runs = 27.9 pc of wins
56.5 -57.5 =10.2 pc of runs =15.5 pc of wins.
58 -59 = 2.7 pc of runs = 4.8 pc of wins.
59.5 -60.5 =0.4 pc of runs =0.7 pc of wins.
+61 = =1.5 pc of runs = 1.7 pc of wins.
hope this is of some help.good luck.