Sibelius 7 is not without it's issues (possible understatement of the day), I have 24Gb of RAM and it crashes still, so I don't believe it's a memory issue. Actually, I have found Sibelius 7 is generally OK, if you work on a song that was created in Sibelius 7, I find it crashes if you continue with a file that was created in a previous version (V6.2 in my case).
Sibelius 7 sounds are a lot better than Sibelius 6 Essential sounds (and will be better once they get the dynamic levels a bit more balanced), but neither is anywhere near VSL.
I have never found a workable way to get my VSL library to work in Sibelius. I have the complete VSL super package, and it is just too unmanageable to work in Sibelius. I guess the SE version works OK in Sibelius?
I would really like to know how to get my VSL library to work in Sibelius (remember, I don't have SE), I did set up my own template once, but it took an eternity to just start up.