How to solve the FPS drop on iPhone4 since Unity 4.3

Overnight, my game went from running at a smooth 60 fps on iPhone4 to a mediocre 35 fps after switching to Unity 4.3. Since then, I've put that problem aside to focus on other things (also hoping that the issue would be resolved in an update) but now, seeing no improvement in that regard using Unity 4.3.3, I have come to the conclusion that I might have to make changes on my side in order to obtain better performances.

I tried playing around with the Application.targetFrameRate value but to no avail (VSync turned off in Quality Settings and in code). XCode keeps telling me that I'm missing my target fps by about 33% (40 fps instead of 60) and suggests that I try to lower my number of draw calls. The highest number of DC I've encountered in my game is about 30 so I don't think this is the issue here. CPU usage is also pretty low at around 50% (25.6 ms per frame).

The game runs at 60 fps on an iPhone4S (as it always has). Changing the targetFrameRate value does not seem to have an impact when running on iPhone4.

Any of you have ever encountered something similar?

Thanks for the help.