Fraser, the fast road setting do improve handling mainly be reducing understeer. That said though, these settings IMO are no more than a compliment to other installed handling mods, like stiffer suspension, droplinks ALK and ARBs (not that you need all of them). I actaully got the settings at the same time the car was lowered, so I can't really comment on the settings alone - but needless to say the change was quite dramatic!
Ask Duncan at Hypertech when you are there and he'll keep you right. They are always happy to help.