I really, really don't agree with these suggestions that there should be a "scale of seriousness" for rape. The comparison to murder or GBH has been made several times and there is a very important reason why these offences are not, and should not be, comparable.
Pretty much our entire society accepts that murder and GBH are wrong. These offences can have anyone as a victim - man, woman or child. A murder victim is almost always seen as a "proper" victim. There is very rarely any suggestion that they might have been in some way to blame for their death. Even the serial prostitute murders were reported sensitively and I did not hear anyone saying "oh well, they were asking for it" or anything to that effect.
Rape is entirely different - there are always excuses. Obviously there are cases where a jury acquits because they simply did not believe that the rape took place - there are cases where false allegations have been made and I have been involved with more than one such case. However, I think there are probably an awful lot of cases where a jury acquits because they think the rape probably did happen but that the woman was in some way culpable.
If murder was to be broken down into levels of seriousness, it probably wouldn't be too much of a problem because it would not lead to people thinking domestic murder isn't serious or anything like that - murder is too well-established in our society as a Bad Thing.
But if rape was to be broken down in the same way, I don't see any outcome but for people to be encouraged to think of some rape as not "proper" rape. I firmly believe that this would lead to a drastic drop in convictions.
Bear in mind that I am a defence lawyer - a drop in conviction rates for date rape would make my job a lot easier as the bulk of our rape cases are date type rape cases. If sentences were lower and juries highly unlikely to convict, these cases would be pretty low-pressure for lawyers. However, I think this would be a huge backwards step in the way society views rape and I would be as strongly against it as I have been against any change in our justice system in recent years.