I've heard the MSD coils are actually worse than stock, so no on that. The GTP coil packs would be a minor upgrade but other than that just leave it alone, unless you're pushing like 400 whp ignition mods really don't make any noticeable difference. I've heard the SLP catback sounds sick, but that's about all it does, there's no performance gain from a catback. If I were you I'd get a 2.5" catted Downpipe for the exhaust which will show some good performance gain, and that will also get rid of your U-bend and include a high-flow cat like you were thinking of getting. Then if you want it to sound good pick up that catback system.
