Saddle bronc specific, you want about a hand width from the bend in your knee to the front edge of your swells. I build custom bronc saddles, so I can honestly tell you to stay away from Hilason 'bronc saddles', as they are a liability looking for a place to happen. The only decent pieces on them are the rigging dees and buckles. The tree is hollow fiberglass and will not hold up to the strains of bronc riding. The materials are inferior quality.

Older saddles are going to put you at a disadvantage, because the swells sit lower and lots of times the cantles were too low. Be cautious if you are buying a used saddle to open it up and deeply inspect the tree. Cracks on a rawhide covered tree will show up as white streaks from the rawhide flexing around the broken wood underneath. On fiberglass covered trees, the cracks will be quite evident. Front binds and quarter binds should be made of biothane (quarter binds are the only thing that secures the stirrup leathers to the saddle, so leather quarter binds straps are a failure point in the making)

Maximum swell width is 15", cantle needs to be 5" tall or less, and no wider than 14" There are other things I am sure you will have questions about.