Keep in mind there are now three models that have been released since the iPhone 4. Each model boasts approximately double the speed, and RAM has significantly increased with the 5. My wife is still using the 4, and the more frequently she uses mine for tasks, the more frequently she notices how VERY slow her 4 has become over time. Any model above the 4 is a noticeable improvement. The 4S runs iOS 7 quite a bit better in my experience, and the 5 is a massive leap above that. The 5S is incredible hardware, but the 5 is super cheap right now via third parties if you want to go that route. There are plenty of reasons to upgrade from the i4, the decision is ultimately yours, but I don't see why anyone would steer you away.