I do a lot of sports and I run and cycle every day. I'm still using my iPhone 4 since its 3,5" screen is perfect size to keep the phone with me when I'm training. Even the iPhone 5 is a bit too big to be placed on the bikes stem for example. 4,5" and 5" is out of the question. I would be happy to see iPhone "mini" and then a larger iPhone 4,5" or even 5" and I would buy them both. I'm afraid that I have to change brand after my iPhone 4 dies or gets too outdated if big screen is the only way for Apple in the future 
Apple, take a not: http://www.nowhereelse.fr/wp-content/uploads/2013/02/iPhone-6-iPhone-Plus-07.jpg
Apple, take a not: http://www.nowhereelse.fr/wp-content/uploads/2013/02/iPhone-6-iPhone-Plus-07.jpg