With our internal tests we saw slow rendering performances opening PDFs files with a lot of high res, not optimized images and pictures.
By the way actually, doing a performances comparison with other available rendering engine we with our PDFViewer has good performances.
Are the magazines you are writing about freely distributable? May you send us one of them? We would like to do some tests on it, maybe looking at others reader again.
To send us big files write a direct email with a download link (our mailboxes should accept 10mb attachments and no more). If you don't own web space and don't want to adopt a free transfer service as wetransfer, let me know: I'll ask collegue to open a temporary ftp area.