OK, I uninstalled every AV cleanly. Installed AIS as a clean install and the load time for it was 88 seconds.
One thing I noticed with just Norton in on snapshot is that while Norton loads in 1 second, the "System" takes 116 (45% of boot time). With avast it was much less so I'm wondering if Norton may not cause that to talk longer to load while taking itself a shorter amount of time. Not sure if that's even possible--just a uneducated guess on my part.
In the total boot time was a little shorter with Norton than Avast by about 15 seconds in one round of booting each.