Indian entertainer pack (for SX700) has size of 132MB and it contains ~60 voices (including drumkits). That means, in this case, one voice has average size of about 2MB -which is very small. Depending on type of instrument, better quality voices usually have size of about 10-30MB (or even more). But you don't need to install complete pack. You can select which voices you wish to be installed.
The question remains: is 100MB memory enough? Yes, it can be enough if you're interested only on particular (i.e. indian) kind of music -because keep in mind, that there are several hundred voices already built in keyboard!
But then, it's never enough memory... if you would like to add some other high quality instruments, then you will only be able to install 4-5 voices -but in this case you can't have indian pack installed at the same time.
We don't buy new keyboard every year, so think twice before deciding.
Bogdan