Fair post i guess ross. Throughout that entire process you have described though, the engine/ecu must do a very good job at containing it all because it is totally non-noticeable engine/turbo/bum dyno wise (other then the che che che noice when coming on boost), or even on a my dyno print. (In terms of my car, ej205, 34, stock bottom end, obvious upgrades)

I was thinking about going P20 - But heard there were very marginal differences hp wise so not been bothered.

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Should have bought an STI

I still think that a simple port job may solve your issues.
The boost creep up top is the give away. The exhaust gases can only go through the turbine or the wastegate, if boost is climbing above target then the wastegate isn't flowing enough. The fact that the p18 is getting 1.4 bar up top indicates that its pretty well sized for the motor (unless you want more!).

You should really only be going for a p20 if your not achieving the boost you want up top. P20 and P18 at 1.4 bar is still flowing the same amount of air through the compressor. 2.5's benefit from the p20 because the p18 wont hold the boost due to the greater flow of the motor, and hence the need for more exhaust flow through the turbine.

As your blurb above states, compressor surge doesn't take into account the operation of the wastegate, and to me it seems silly to give up response without first trying to fix the wastegate problem.

Here's a couple of log screen shots that show my issue.
White = boost
Yellow = Airflow
Blue = RPM
RED = Knock

The image below is a gate pressure 3rd & 4th gear pull.
Note: the small 'V' in the top left of the airflow curves - that is compressor surge, also shown as jagged boost at the same point & slight burn instability shown by the slight increase in noise on the knock sensor line.
Peak boost is 1.44 bar



This short pull is how it is now with the EBC set to trip it's overboost function & revert to gate pressure @ 1.1 bar. This is why there's a notch in the rate of boost increase on the left leg of the boost curve, this little notch is enough to prevent the compressor surge.
Note: Smoother curve above surge point & lower knock channel noise.
Peak boost is 1.6bar



AFr's are 11.0 - 11.4 on all runs and lag is non-existent (nearly vertical boost climb).

Compare that boost response to the old stock version 6 ej207.....much slower boost ramp rate when compared to the new built motor.

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[CENTER][COLOR=#ff0000]Built Ej207: Semi-closed RA Cases - Wiseco Forgies - Manley rods - BC 272 cams - GDA Heads - billet f/whl - Vi-pec - WbO2 - 800cc Yellow tops - TD05-20G - 409Hp ath @ 1.75bar on E85[/COLOR][/CENTER]