****************, I have some stats somewhere that 70-80% of all handicaps are won by one of the top 6, and 80% of winners carry within 3.5kg's (up or down ) of their set weight last run ( disregarding any apprentice claims) and also; ran within 3.5 lenghts of the winner last run, so seems to me that you are on the right "track".(dare I say no PUN intended there??)

Just a thought, but you could also look at any contender having a win in their last 4 starts and of course racing within 21 days, and maybe even a miniumum place record of at least 50% (optional)