In reply to alamik:
The answer, of course, is; it depends! If you want some numbers I believe the winter grading for ice climbs is explained in the intro of the SMC guides and steepness of the hardest sections is given. Up to 70 degrees for short sections on grade III I think.
IMHO you need to have some basic ice climbing technique to be safe leading a grade III. Grade II you can normally get away without much experience of pure ice climbing (vs steep snow climbing), as the pure ice sections tend not to be that steep or sustained. Of course any grade II in lean conditions may be harder, eg Gardyloo.
Tower Scoop has a bit of a rep for being steeper and more sustained than expected, so if you're in any doubt it's probably not one to "go for it" on. The other thing to factor in is how much traffic the route has seen - a ladder of steps up Green Gully will for sure be easier than unmolested ice on Tower Scoop!