I do about 7000 or 8000 mile each year. This car is a daily runner, what is annoying me is I have been making modifications to the engine, but it refuses to rev up.
Anything higher of 4500-5000rpm is very difficult to achieve, even at 5300-5500 the engine fails, like if it were rpm limited.

I think with my actual spec, the engine can rev up to 6000rpm without major problems.
My actual spec is:

Twin 40 DCOE
Facet silver top 200bhp fuel pump
Newman Phase 1 cam
Slightly worked head (not hemi)
Exhaust manifold from a xr3i MFI

A pic of my engine: