It is normal that new iPhones 6 and 6 Plus are the largest and the fastest in the whole family, and it is very interesting to put all Apple's phones into a video and compare their speed. People standing behind the channel named "EverythingApplePro" on Youtube, and the results might surprise you. 

If you have ever wondered which iPhone will boot fastest, the answer is 5S, and after that, iPhone 6 and 6 Plus, and original iPhone is right after them, in front of other, newer models, because he is the oldest. iPhone 5 will boot latest, and the reason is that iOS 7 wasn't still "settled" in this model. 

Every model passed a Geekbench test (except the first iPhone and 3G model that doesn't support it). Model 3GS needed 15 minutes to end the test, while iPhone 6 Plus did it in only one minute. 

Take a look at the whole test, here.