Should I have two nibs to give support to the screens for iPhone 5 / iPhone 4?

I started to work in an App that needs to be optimized for iPhone 5 and requires iOS 5.x or later.

But the scenario where the user has and iPhone 4 with iOS 5.x is possible. But the Autolayout will be a problem on those cases...

So, I could use Autolayout for iPhone 5,but the users with iOS 5.x(iPhone 4 or below) will have problems, so in order to avoid that, should I have two nib's one for give support to the iPhone 5 screen and another iPhone 4? (And that sounds very ugly to me).

Having something like this...

if(IPHONE5){
//Load iPhone 5 nib with AutoLayout or without it
}else{
//Load iPhone 4 or below 
}

In any case, is there a better option to give support to both screens but with different iOS versions? suggestion on this?

Since now thanks

Solution

This is something that I had been wondering about myself. However, I stumbled upon a webpage: "Drop iOS 5: Only support iOS 6" that explains that such scenarios if possible, should be avoided.

Doing development for older OS's might seem reasonable, however...

the rate in which people update their phones is extreme fast (unlike Android)
the development time increases
development costs increase
maintaining code more complex
release dates become later

as a result:

more people have upgraded to the newer OS
your 'older share' has become less relevant
your 'lost sales' is even smaller
your 'return of investment' because of increased cost has extended

My advise: drop iOS-5