I also find this topic intriguing because I cant get much rpm and a lot of people comment on how quite my car is compared to most GN's. I have fixed the cat so that's not the issue now I wonder if some old cat **** got into my mufflers and clogged the system? It almost makes perfect sense because I cant get over 4200 RPM and I've done everything pulled the oil pan and it looked perfect the cam looked good the pistons looked good. The coil pack is good. This is my latest idea to check out and I think I might have something here. because when getting on it I get a slight wind or hiss from under the car that I never thought a lot about until now.
I'll report my finds after I disconnect the downpipe from the exhaust and see what happens.
Just a update it seems exhaust systems can get clogged as my car preformed much much different with the open exhaust. I will update this once a new exhaust system is on the car to prove if this is true or not.