Someone posted a comment on my last post asking whether query layers were slower than spatial views. To be honest the occasions I’ve used query layers have been for small focussed queries (i.e. nothing that was performance critical) so Ive never had any performance issues with query layers.
However I ran some tests using MXD Perf Stat between a feature class (stored in MS SQL Geometry), an old school spatial view and a query layer.
The results show that a spatial view is very close to the feature class while the query layer is a bit slower (especially at smaller scales ie > 1:50K).
Below is a chart from the quick tests I ran.