I don't think there are any really solid approaches here except to use IRHydra [0], which lets you decompile v8's optimized version of a function into an assembly-like representation. But I'm pretty skeptical of whether anyone but v8 engineers can really make use of it.

I think the only workable approach is what you're doing - have an approximate idea of how the compiler works and make intelligent guesses about what will help. But when you're tuning at the level where changing the order of if statements makes a difference, you're at the level where next month's update may reverse your fix, so in a lot of cases it'll be questionable whether it's worth the effort.

[0] IRHydra - http://mrale.ph/irhydra/2/