if your $5K/mo comes mostly from Google traffic you can lose everything overnight.
i.e. I have a friend who had an affiliate site that was generating $20K/mo. Then the Google Panda update happened, and that went down to $1K overnight(well it took a few weeks). Last month that site generated a whopping $24 in revenue.
Google tends to be the biggest threat here.
Traffic? Can't lose out in Google search results.
Ad Revenue? Can't get banned from adsense(impossible...since all it takes is a competitor clicking a bunch of times on your ads)
Paid Traffic? Can't get banned from adwords...which can change their policies at any time.
Payments? Can't get banned by PayPal.
Basically what I'm trying to say, is that there is a TON of risk. And you need a huge cushion to feel comfortable. Personally I'd want a $30K/mo income in order to have a $4-5K/mo lifestyle...just to be on the safe side. To at least avoid the stress...that everything can be lost overnight.
That's why these big payouts should be preferable...since then there is no more risk(short of losing it all in financial crash)