When is flotation gear legally required for pilots and passengers on a non-commercial flight in a small airplane over water? If I'm renting an airplane to fly myself and some friends over water beyond gliding distance, but within 50 nautical miles from the nearest shore, am I legally required to have any flotation devices whatsoever?

According to 91.205 if you are flying for hire over water you must have life preservers for each passenger. However, does renting an airplane for recreational use trigger this requirement? In other words does renting and aircraft from an FBO qualify as operation for hire for purposes of section 91.205?
Apparently, the answer is never. 

After several days of searching, I was unable to find anything in the FARs that requires the pilot of a small aircraft that is NOT being flown "for-hire", to have flotation devices on board, for a flight over water, regardless of the distance from shore. 

Section 91.205 requires flotation devices, but only for flights "for hire" over water. So this section doesn't apply to this question.

Then, there is section 91.509(12) which requires flotation and other survival gear for flights 50 nm, or 30 min out from shore, but this entire section is under Subpart F - Large and Turbine-Powered Muti-engine Airplanes and Factional Ownership Program Aircraft. So this entire section doesn't apply to this question either.