The champ and star Leos will definitely be more stable...durability is different, of course, but the premium plastics shot into molds that were designed around base plastic tend to fill it differently and thus change the flight qualities a little (the plastic density also affects this, as does a mold that is worn with use). A new champ Leo will be vastly different from your worn dx. They tend to fly very straight and are much more difficult to get to turn without a lot of power or some anny. Champ takes forever to beat in, too, and it won't quite get you to the point of a worn dx. Star plastic would be a better choice there...still going to start out pretty stable like the champ, but it'll break in faster/easier. Good rule of thumb when stepping up to a premium plastic from a base plastic mold (which is unfortunately not absolutely accurate, due to run variations in the discs, but a good consideration anyway) is to drop down in weight 5-8 grams or more....or choose a mold with similar flight ratings but a notch lower in speed.
If you aren't stuck on Innova, there are several great premium plastic discs from other companies that would probably fit the slot you're looking for. Some info on the distances you're getting with current discs, the distances you want to get with the new disc, and flight pattern you want to see will help pick the best fit. Harder to get some of them in those ultralight weights, but some are available, or if you aren't totally opposed to the normal heavier weights, you can still get what you're after, one way or another. If you can find a really light champ Leo, it may give you what want, but there are tons of options.
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