We're not noticing any major difference in preset loading speed or volume dropout on the latest build 5.2.0. If anyting it may be a bit faster than in version 3 with the same dropout.
Loading from one preset/algorithm to the next can cause a perceived lag and volume drop depending on the settings. Is there anyway you can do a controlled test, switching using the exact same presets but on the different OS versions? It sounds like you're using custom presets vs Factory. Also if your mix values are high say approaching 100%, you'll notice more of a dropout.