I don't believe a Sandy Bridge CPU is less heat over time because it used an older (larger) process for manufacturing than what Ivy Bridge used. Maybe those 65W and 77W numbers are misleading about how much power the two models will actually use?
You can kind of cool things passively, but not really. You do need at least one rear case fan in the system.
If you then use a tower cooler, you could improve things by making your own fan duct that connects the tower cooler with the rear case fan spot. It would then be guaranteed to work well. In a setup like that, I think I'd try installing your single fan onto the cooler and not as a rear case fan. The sound will get muffled somewhat if the fan is hidden deep inside the case.
Take a look at what your motherboard's fan control settings are like in the BIOS. You perhaps have very good controls where you can freely choose min and max speeds and a fan curve. Or maybe you can choose a fixed, low speed. A fixed speed will work well with a stock settings CPU if you have a large enough cooler with heatpipes instead of the crappy Intel stock cooler. If you can limit the max speed of the fan, you will probably not have anything to worry about. There's cheap fans from Arctic that are a good choice if you find out that the fans you currently have are producing strange, annoying noises at low speed like a ticking or whining.