A couple of people have mentioned that levels load faster when you are running a custom HUD. After a bit of testing, it certainly seems to be the case on my PC. On many of the larger levels the load sort of hangs for a few seconds at 60%, but with a custom HUD this pause goes away or is at least greatly reduced. On smaller levels like ATCS it won't make much difference, but on levels like transit and nexus there's a distinct load time advantage.
If you're easily able to disable and re-enable custom HUDs, please test it out and see for yourself, and post your results. Any devs or otherwise code savvy people have an idea why this might happen?