once reqstats is in a better/more reliable state than sqstats.pl (i.e. T83580) we should get more signal out of reqstats metrics by e.g. look at ratio between errors and requests and thus have a percentage to alarm on, e.g.

http://graphite.wikimedia.org/render/?width=736&height=379&_salt=1430989607.95&from=-2hours&target=reqstats.5xx&target=reqstats.500&target=alias(secondYAxis(divideSeries(sumSeries(reqstats.5xx%2Creqstats.500)%2C%20reqstats.requests))%2C%22(5xx%20%2B%20500)%20%2F%20total%20requests%22)