Originally Posted by asgelle

Changing to an aero wheel in the rear will lower drag by ~75% of what would be seen putting the wheel in the front. Riders put a deeper wheel in back because the rear wheel does not affect steering stability, and adding surface area to the rear actually makes the bike more stable.

Originally Posted by AdelaaR

What kind of performance are you after?
Are you wanting to shave about a second per kilometer to do better at your next time trial?
If that's the case: go for it.
If you're expecting anything drastically more than that you're in for a dissapointment.

Originally Posted by FlashBazbo

And also, the manufacturers only say aero trumps weight IF the wind direction, relative to the bike, is within a certain narrow range.