I use symbology classes to display my data most of the time. I think I have noticed a performance hit when using symbol classes on large datasets, although it might just be in my mind.
That got me to wondering is it more efficient to 1) symbolize a single layer by categories or 2) create copies of the layer with definition queries in-place and symbolize them as a single symbol.
Setting up definition queries and setting their symbology would take time but I would do it if it gained a performance boost overall.
Also, looking at the second to last point in Best practices for using layer definition queries... I saw:
A definition query cannot be set on a system field while creating features
That would make me lean away from option 2 even if it does have better performance.