Ive opened up a thread on the twincam forums asking other people what they're setup is.
So far it seems that 5000rpm is normal because of the 4agze not being a very well flowing design. Only plus side its got is that it will be reliable...Im very much in favor of reliability. The 20valve motors with 5 valves per cylinder is the far superior motor for boost, although you have to do a lot of preparation work.
Next modification I think is change to the 20valve head
Peoples setup:
3rd gear at 90kmph is 4500rpm, which is where the power starts to pick up
4th gear at 110kph around 4200rpm.
Very similar setups, they are just running more boost.
I guess the engines are just laggy.