If you are going to go with a HPR 06 or any quality large cat hull then twins are a must.
This is for the simple reason that if you have spent that much on a hull then do not skimp on the power, go for twins.
I do not have a twin-cat.......yet
When I do I will design and build my own, long story there.
I have done a LOT of research on twin setups for cats and can advise if you like, Jan (pompebled) will help too.
There is a LOT of info over at OSE on twins and the HPR hulls in particular.
PM me if you need some links or further info.