I have been reading all this about the ISI cabinets and it is making my head hurt. All the technical stuff and what a chart says it will do and what it will not.
I have a Crazy 88 and I found a used ISI at GC - so I bought it.
They both have great tone and actually sound about the same - However the ISI will go much louder for one cabinet and the bottom end pounds you in the chest.
The ISI is a bit heaver than the 88, but both are great cabinets and the 88 will do the small and med gigs (one 88) and the ISI (one cab) will do the larger gigs that a club in town will be.
I use a TC 250 on the 88 and a Mark 800 tube on the ISI.