HiSway bars aren't the issue. The car was an XR7, so it has the largest factory sway bars. The MarkVIII did pretty good, but once the straights came up I was just walking away from him hard. The guy who owns the Mark said to me later that day that if my car had good brakes and tires it would be a menace, and he would try to stay out of my way!
Looks like you really need to upgrade your brakes too. I'm surprised you are still running the stock single piston calipers. We went to the twin piston PBRs right away, but clearly that wasn't enough. Now the only decision I have to make is whether to go with the twin piston 13in brakes, or to jump right to the brembo 4 piston calipers at $1000/set.