Icarus eXcel (M92) and PDFs
When I bought Icarus eXcel (M92 rebrand, launched on 2012, 800 Mhz processor), I thought it would be much faster than my old Kindle DX (bought on 2010, 532 Mhz processor). However, it's exactly the opposite: PDF files take more time to be loaded, and eXcel is slower when changing (refreshing) pages.
For instance, a 7.8 Mb PDF (scanned pages, 300 dpi, b&w, landscape view) takes full 3 seconds to refresh a new page. Kindle DX takes a bit more than 1 second to do the same job.