I handled a 4,3 Mb ePub on my Acer Aspire One just fine (well it took Sigil a while to load and save) This book has more than 1000 pages.
How long did it take for you to save the file? When i do it i leave it for more that 20 min and still nothing. Perhaps its my file?
I still need to create a new issue tracker not had time. will do it this weekend.