they're not the same mold, but when a gazelle gets broken in, it will fly straight. and when it gets broken in even more, it will make a really nice turnover driver.
since the leopard and sidewinder don't have stabilizers (notch or bead or concave wing), they're not good into a headwind, and since the gazelle is so light, it's not that great either (it does have a notched wing, which helps). so, that's the reason for recommending a heavier gazelle.
once that starts finishing more straight than left, you could drop the leopard and get a new gazelle for the somewhat-overstable slot (and you *will* want to, because that broken-in gazelle will be your favorite disc

).