I rarely fish sinking lines, but I understand from Chico F. that *sometimes* it can be benefical to use a longer leader with one over deep, spooky fish. However, for most people and in most cases a short 18-36" leader works best (I use nose to fully stretched arm....similar to dry fly tippet). The longer you go with a leader on a sinking line, the more you're working against the purpose of getting deep.
I'd rather fish a floating line with a weighted fly than a sink tip with a prepackaged (fairly long) tapered leader.
Gene