The rational is the same as switching more stocks to bonds as you get older, you have a lower risk profile because you don't have the time to make it up.

Personally, I'd prefer to option the property.Due to the extended time period and changing circumstances (and the input from others' influence) there are too many reasons tgat may cause a seller to either not perform or to rationalize bouncing out of escrow. 

Just to make sure there is a rational counter perspective, here are some reasons why and when it might make sense to use private money instead of hard money:1) Maybe it's your first flip but you are experienced with renovation costs and/or are a contractor and have a good handle (or help) with total costs and re-sale values.  

I own two homes and therefore I am unable to get another mortgage under my name due to debt to income ration on a conventional loans.  

Is the accounting easy enough to do by oneself (is the ration time/effort to cost worth it ?) 

http://get.biggerpockets.com/flippingbook/What you've asked is a question that can't be rationally answered in a simple forum post.  

I live in a class A area where the rent ration is about 0.7% only.  

Don't let your rational engineer-type brain get in the way of understanding what other people want and need, and what they'll pay you for it.  

dang bro that's alotta paper u buried in.. id cut up cards and focus on bringing that DTI ration DOWN!

If rental income drops you know why, its rational.