In your car and mine, you can disable HICAS by tricking the PS fluid sensor. Henri Le Hir has a post on how to do this I think.
I suspect with HICAS you can keep most of the benefits of understeer (putting down extreme power on corner exits without spinning) and still have some of the benefits of near-zero understeer on corner entry (getting some nice slip-angle in the back). Again, I have to try without HICAS to see for myself, and I have to freshen my tired old suspension before I'm likely to notice...