I just installed it on both my 5 and 5s. It does seem faster but my iPhones have been faster for me since yesterday when I had the phone company tweak my router. So I'm not sure if the increase in speed is the tweak or 9.3.1.
My 6 Plus did seem to slow a tad going from beta 7 to public release of 9.3 but 9.3.1 has now brought it back to being as fast as beta 7 so am a happy camper so far with 9.3.1
after using 9.3.1 for a day or so now, I can say it's great! my animation issues seem to be gone and the phone is very smooth and fast. I wasn't having the Safari issues, but overall this is a GREAT build!