What did you do about the phone? Hopefully a new battery?
FWIW, my iPad 2 still runs like a champ on iOS 7. And will continue to do so as iOS 8 doesn't bring enough to the party to update on that model.
I kept it for a while longer, then someone gave me a broken iPhone 4 which I got replaced by Apple with the out of warranty replacement
The 3GS is still my backup phone, and it goes everywhere as it has all my Music on it that doesn't fit on my 16 GB 5. Sadly a few months back, the battery expanded, but I replaced the battery myself and its good now.
iOS 8 will start to bring more to the table when Yosemite and is released and Apple enables more iOS 8 features. My main gripe is iOS 8 doesn't allow for iPhoto to run and I really need it. Also performance of course is downgraded.