Ben, I'm running 17psi too, with overly rich fuel and little timing. But forged pistons will be going in soon.
Steve, Can you get the manifold flow tested? Be interesting to see if it is causing interference.
Don't bother with compression test, that will tell you nothing, do a leak down test, this will give you a much better idea about engine condition. My car has broken ring-lands, still makes over 400rwhp:D
JimX, With factory cams I found that 0 was the best setting for my adjustable cam gear, it may be due to the fact that the factory tolerances for the standard nissan cams mean that there already perfect:D
Steve, Sorry to here about your dramas:( I have a custom manifold with a GT30 (0.64housing) and it's making over 300rwkw. Mine is still stock cams, stock headgasket. I'm personally not entirely convinced that it is the manifolds fault, as my mate has the larger housing on his and it's not nearly as laggy as yours.
Yes, it is tractive effort, not sure if it can be converted back to engine torque, but at least you have a comparable figure to see what effect mods make to the tractive effort.