Upgrade to iOS 8

I'm excited for iOS 8, but I'm thinking about not to upgrade iOS on my iPhone 4s.

Ios 7 slowed down the iPhone 4 and I'm afraid this will happen to my 4s too. I have also have an iPad 2, but I don't think it will get iOS 8. A friend of me still has iOS 6 on his jail broken iPhone, I couldn't believe how fast it was.

What are your thoughts?

Does apple just want people to buy a new iPhone because old ones are barely useable with new iOS upgrades?