Thanks for the helpfull comments Terry, you are correct in fact using wieghts i have found it really only gets intetesting in the longer races and the jumps so my approach focusses more on jumps using weight. Flat sprints dont seem to lend themselves to wieght too much.
I just tried using wieght on flat sprints and only found 5 1/2 f had any merrit with approach i use. So not really a big pool.
I can see why you use speed figures for sprints makes sense.
As you say for other races wieght becomes more important.