My new mac has:
2.2GHz Quad-core Intel Core i7, Turbo Boost up to 3.4GHz 16GB 1600MHz DDR3L SDRAM 256GB PCIe-based Flash Storage Intel Iris Pro Graphics Force Touch trackpad Backlit Keyboard (English) & User's Guide Accessory Kit
But when I scroll this (or other pdf) in safari link
it looks not smooth when you scroll it. But my mac book MacBook Pro (13-inch, Mid 2012) has smooth scrolling.
Actually on my new retina mac if I open gmail via safari and try to scroll over 20 emails in list it also stuck when scrolling. Like it's from 1995 years computer.
So I tried it on 10 computer in apple store and all of them have the same problem when scroll link above or gmail content in safari.