iOS6 doesn't run at a solid 60FPS on the iPhone 4. Just go into setting on both your 4 and 4S compare how well each one scrolls.
It scrolls fine, while I will grant you the fact that I *think* the 4S is slightly faster than the 4.. they are both pretty slick/fast.. anyone who thinks the iPhone4 is 'slow' (as I said I'm not sure I can even tell the difference..), but pickup an old Android phone, they don't age as well.
I have an iPhone4, 4S, HTC Thunderbolt and a Samsung GS3. The only turd in the bunch is the Tbolt, all the others are great devices. I like them all and couldn't give 2 shits about Android vs iOS. F**** Apple and f**** Google. Don't care, they don't pay my bills.
I do regret buying the Tbolt, I should've gone with the 4S at the time.
I'd probably caution people more against Android, because you don't know if you're going to get a 'HTC Thunderbolt' or a 'GS3'. While the old iPhones are still simply great. That said, I can't speak poorly of the GS3 without lying through my teeth.
I'm also not going to lie about the iPhones I have either. The iPhone4 kicks ass to this day.
Truth is all relatively recent iPhones are great, and always were. A good, well-supported Android is also kickass. I prefer Android for work phones, iPhone for personal use. The iPhone5 is the ideal size for a smartphone in my opinion.
I'd use either though.