YMMV as it depends on the document(s). A very large (279 Mbyte, 11,800 page) test document did open more quickly in Adobe Reader 9.2 (5 seconds) than in PDF-XChange (10 seconds). However, drag and drop of 15 average documents was a different story entirely.
Adobe Reader opened each one in a new window (how do you change that?) and took 30 seconds, PDF-XChange opened them all in one window and took 5 seconds. Of course, closing 15 windows was much slower than closing one window.
You might also try some simple searches of multiple documents.
My results indicate that Adobe Reader is a snail compared to PDF-XChange, and the light-weight and light on features Foxit Reader find fewer results than PDF-XChange.
Adobe Reader has a maximum of 10 recent documents, PDF-XChange can remember 50, and has options for managing the recent file list.
