I autocross as well, and honestly I wouldn't do it with an SVX. They
can be driven fast, and I've been surprised by how well they scoot around a course. But it wouldn't be my first choice. The SVX is heavy and complicated and you're going to pay for more repairs. I'd rather put my money into tires and other necessities.
But that's just my call, based on my situation.
From a competitive standpoint, the SVX is in the same class (GS) as the Mini Cooper S - the supercharged one. I haven't seen the two cars go head to head, but I know which one my money would be on.
Don't get me wrong - I love my SVX. And I know which I'd rather take a 120mph+ road trip in.
But a tight and twisty autocross course?