First, you won't get -50c with a Vapochill, the temp readings on the Vapo's are notoriously inaccurate and always read colder than they really are.
A Vapochill, or almost any single stage phase unit is not made for all out benching. They should be used with moderate vcore, about the same as you would run with good water cooling, the benifit is that the cold temps will give you a much better oc than you can get with water; IE: if you can get 4.0ghz @ 1.45v on water, you can probably get 4.5ghz at same vcore with phase change. (this is just an example, results will vary).
@DaMulta... not all 6ghz cpu's die after testing, this is a popular misconception. I have the world record for Pentium D 950 Presler at 6.1ghz, this was set a couple of years ago using dry ice cooling, that cpu was benched hard for a couple of months at very high vcore and a few months after that was installed in a pc I put together for my brother.... it's still purring along at 4ghz to this day with no ill effects.
So far, I've never killed a cpu by benching and most of my cpu's end up in daily use pc's when I'm through with them. I have killed a few gpu's though, mostly from condensation though.