There is no rule, to many factors in everyday life such as car payment, bills, phone, insurance, food, kids, etc so to say rule is X% or 2 weeks pay or whatever doesn't always work.
It's very simple and I can not begin to understand how the average adult can't not determine how much money they bring home vs the Bills they have going out. Maybe I am to nieve because I have always been perfectly able to budget my money since the day I began to work at 14.
Love it when I see people talk about being broke but have a project car or the newest cell phone etc but can't go out and enjoy one basic $20-30 night with friends because it's tiesday and they don't get laid until Friday.
JP- better question for you sir (because I am not married) how does your wife feel about the situation and how big of a factor is that for you? Does she say you work your ass off and go for it or is she reluctant not knowing for sure the future? I think this plays a huge roll on the conscious of ones decision