I think your best bet would be to either use any of the eInk devices mentioned in a post above that can display ppt files or output the ppts as jpgs or pdfs so they can be used on an eInk device.
I'm happy with my Sony readers but prefer my ipad for non-novel-stuff.
But I have to admit, too, that after a day at work (mainly screen work) and being tired in the evening, reading on the ipad where I really have to concentrate on the text isn't my thing either. So during the week my ipad is more like an on-the-sofa-surfing-machine and a magazine reader for the weekend.
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