Lokt, i don't know a lot about this but i can try to answer with my knowledge :]
Think about Genesect. He got download so you use it with uturn when you get the att boost and you use an special att move when you get the satk boost. Know, a good spread for Scarf gene was 8 Atk / 248 Satk / 252 spe. The 8 evs in Atk allows him to get those bonus points when he gets the atk boost, now, i dont know how does it work but i know that you get extra points. Is that what you were looking for? Sorry if i didnt have the correct answer :[
Are there any tools that help with EV spread efficiency?
What do you mean by tools? Because if you want to know which amount of speed evs should your "x" pokemon run to outspeed certain threat you can use smogon strategy dex.