Thanks for the reply. The drives / peripherals in the system are identical; only the MB and CPU were changed, so not sure why there weren't driver issues before if there are issues now...
The MB driver or BIOS could be problematic. It's very complicated, covering many different functions of the chipset. Maybe you can play with BIOS settings, there could be settings that slow down boot. See if "Load Optimal Settings" BIOS option helps a bit. And regarding drivers, sometimes older drivers work better than newer ones. Experimenting with BIOS and drivers is very time-consuming though.