This question is usually answered as "it depends" to quote
Rick (Captiv8r). The reasons are as follows:
My biggest single project ever was 187 slides of a software
solution sized at 1024 x 768 and it ran like a dream.
I have heard of projects of 80 slides crash that were built
to same spec as the above.
There are too many factors that can influence your potential
maximum size thus it is impossible to dictate what is too big and
what is not. The general rule of thumb though is try to keep below
about 80 slides if you are going to be loading each slide with
interactions, captions etc.
My advice in your situation would be to see if you can't
break your project into logical chunks and build in a modular
fashion, you could search for "daisychain" in the forum and follow
Rick's advice as given there to keep your modules linked.