I have not used iphone 5 neither 5S, i bought 4S back in 2011 when it was launched, then switched to android (samsung galaxy S3 GT-I9300) because of large screen size, used it about 3 years, then i purchased iphone 6 (ALHAMDULILLAH) ...
About performance, well it is definitely an improvement in newer models, but i would suggest you to go for it atleast 5S if you want to upgrade ...
Sent from my iPhone 6 using Tapatalk