The purpose of holding Vanish is to use it when Envenom has fallen and you need combo points in order to refresh it, in other words to try and increase Envenom uptime. I do wonder though, given how small a dps gain that is, if it would be better just to use them both in the opener to increase burst like you say. That is what cute's profile does, whether intentional or not, it does seem to help ensure you go into Vendetta/Blades with full energy. The downside to that is if you do get a Relentless Strikes proc plus maybe a Blindside proc your Vanish is more or less completely wasted.
Using Cooldowns straight after the SnD goes against all theory-crafting I've seen, and the Vendetta global delays your Rupture application.
Tomorrow I'll try a build with the energy pooling on the opener, as long as it's not pooling for more than 2-3 seconds I suspect that would make the opening burst more consistent.
I might also try some logic which Vanishes for the second Mutilate if we didn't get a Relentless Strikes or Blindside proc, could get a bit complicated though.