Straight LW Shockproof FTMFW! Greatest stuff for WRX 5 speeds and pretty damn good for the MT6 in the STI.
Sue's wagon sucked big time until we swapped in shockproof.
F' the diffs,

The synchros will fail long before the diffs is the theory and shifting smoothly is a whole lot more fun than not. I'm actually not convinced the diffs even care based on the very low speed differentials they operate at. As long as it doesn't affect the LSD/DCCD functions, I'm all about protecting the things that take the most load/impact, the transmission.
Don't even bother with the "Cocktail". Too much cost/effort for what? No science that I have seen, and just as many complaints as accolades vs. straight shockproof.