ShadowKiller doesn't do what Zero wants to do, I don't think. It effectively makes windows borderless, which is really ugly and really annoying.
If you mean you want to eliminate the translucency in menus and in window title bars, there are some OS X theme hacks that change it so they are totally opaque. I don't believe this will give any speed boost, though, as the Quartz layer still has to do all of the calculations of the appearance of the menus this is usually just for aesthetic enhancement for people who can't stand the transparency.