Found this via Google:
http://www.imazda.com/forums/showthread.php?t=509
It makes sense that changes in track width would affect handling, although I don't have the expertise to say why and how. Someone like HACK should chime in here.
Also, the option to get wider wheels should also be considered. Rather than getting a lower offset 8" wide wheel, you could get a 8.5" ET 41 wheel to maintain the same inner clearance while extending the same 12mm outward.
EDIT: Might be worth putting in a call to TC Kline or Fall-Line or anyone else who would have some racing experience with these cars.