Revaluate Default JVM tuning parameters

It's been found that the old twitter recommendations of 100m per core up to 800m is harmful and should no longer be used.

Instead the formula used should be 1/3 or 1/4 max heap with a max of 2G. 1/3 or 1/4 is debatable and I'm open to suggestions. If I were to hazard a guess 1/3 is probably better for releases greater than 2.1.