boost
I think 8 is kinda low. Mine when I got it only had around 9, but later found out from taking the intercooler lines off and putting them back, due to doing the head gaskets, I must have had a leak, because afterwards my boost was up to about 12. Also, I'm not sure, but I think you should have done both cats. The side with the high flow is breathing more than the other side, but I don't know if this would affect performance. If you can afford it, I'd have the other one replaced with a high flow too and check for some vacuum leaks. You can do that by spraying carb cleaner around the vacuum lines and super charger connections (intercooler lines) and if there is a leak, the idle should go up.
Good luck on it.
David