Hi Rangi
I've always used Sibelius to notate, although i have Logic Pro x I've always found that the score editor was really bad compared to other options. For example, i could never get on with the way it desplays the staves, as to get a good view of the stave i was working on i'd have to enlarge the screen so much that i could'nt see the time line very well, and to see the whole score was a right faf.
Also, i found that once id written my score and imported it into Sibelius to make fine edits, it would do silly things like tieing 2 quavers together (not showing a crothet) and once id gone over the whole score it would have been easier just to have started in Sibelius in the first place.
For me Logic is superb at sequencing. The drum editor, arrangement track, and the way it generally handles Midi is superb, but for composing with a score, for me its not the best option.
I use Sibelius for composing the score and parts and use VSL as the play back option. I then export the midi into Logic for tweaking the playback. I have to say though that ive spent ages with Logic trying to get the playback as good as i can get it, but lately im finding that the playback with VSL and Sibelius is lovely (it takes a lot of careful hidden dynamics changes for sure!) and im beginning to think i'll give Logic a miss completley (unless im writting rock and roll stuff for my band then Logic is an absolute no brainer!)
The best thing i can suggest is to do a short test piece, export as either midi or XML into Sibelius and see how you get on
All the best mate
Paul