Are you able to test the "ComponentOne XAML controls" demo from the Windows Store for these PDFs? That way we can compare to see if maybe the specific device causes a slower load time.
For me running this app (select PdfViewer and load the pdf) on a Surface RT (2 GB RAM), the Albanese PDF loads instantly and the TestingForContinuous… PDF takes 7-10 seconds to load. It’s true that we will use a close font for any unsupported font, but the run-off text is an unsupported issue. It’s possible for us to fix this in Windows 8.1 if you decide to upgrade.
But regarding the images appearing black that will be impossible to fix in Windows 8.0. We can’t support every image encoding fully using our default rendering approach. In Windows 8.1 we are able to use a system rendering approach. You can read more about this here: http://our.componentone.com/2013/11/15/pdf-rendering-windows-8-1-api/
Regards,
Greg