1) go into view > textures and set both the desk and the paper to "Use color" (textures ramp up the cpu's graphics work?)
2) go into view > smoothing and set the slider all the way left to "none"
3) in the play menu go to playback options turn off the Kontakt player that comes with Sibelius 3, or don't install it at all.
The Kontakt player that came with Sib 3 only gave me headaches anyway and the instruments next to GPO were basically uglyrific
I think these tweaks cut out a big chunk of unnecessary workload.
4) also I was going to set up with sounds on external HD and everyone I talked to said not necessary and probably not even good
Hope somebody finds those helpful
Also, when you get everything rolling break out the limoncino or the 20 year port and drink a toast to Gary Garritan et al