GBH with intent carries a maximum sentence of life imprisonment. While the exact circumstances of the 'Section 18' offence alone might not meet the criteria for such a sentence, it's likely that (with such a catalogue of violence) the judge will want to pass the 'next best thing'. The judge also has a duty to protect society from the actions of the offender. With those points in mind,
I can see no alternative to an 'IPP' sentence being given.
If you're unfamiliar with IPPs I'll refer you to the HM Prison Service website for an explanation:
http://www.hmprisonservice.gov.uk/adviceandsup port/prison_life/lifesentencedprisoners/
It's unlikely that the IPP tariff would be less than 8 years. It's more likely to be around 12 years. But, as explained in that link, the offender might remain in prison for substantially longer.
Chris