I haven't experienced any lag in any scrolling whatsoever on stock settings, although I am trying out a 0 hotplug configuration that I used on my Nexus 5 which is underclocking the phone while keeping all 4 cores on. Even with stock settings, I didn't experience any lag.
Definitely give it a try, I am using ART as well.
This is the config for those who don't know about the 0 hotplug config. I don't take any credit as it was posted on N5 forums way back. You can change the settings via FKU app.
Min CPU Freq: 300
Max CPU Freq: 1267
GPU: 330 MHz
Voltage: Underclock values depends on what kind of binning you have, figure it out or leave it stock. Takes time to tinker around to get stable undervolt values.
sync_freq: 960 MHz
hispeed_freq: 1190 MHz
These values can probably be tweaked around so it suites the OPO better but it should be more or less the same as the settings from N5 are the same. Battery life is insanely good. And don't forget to set on boot.
Frankly, some people just don't notice lag or choppiness when they see it. Try installing the Slickdeals app and if you don't see lag there in the main deals feed on the OnePlus, then you just aren't sensitive to it.
Like I said before, some apps are smooth and okay. The launcher and Chrome run smoothly on the OnePlus, which are probably the most used apps, but a lot of the apps I use don't run smoothly at all compared to the Nexus 5.