So... I can purchase a four ship of vipers, and fly them AS A FOURSHIP for 20% longer than a SINGLE F-35.

Fifth generation stuff is fantastic, but not if you can afford it.

EA / new radars / new motors / new missiles to fourth generation jets and the US will be able to TRAIN and equip our air force for the next decade or so. My $.02

Kill the F-35 - maybe we can salvage some of the R&D... It's called a sunk cost.