Dump pipe installed today. And all I can say is WOW... This has been mentioned several times on the forums already, but I'll say it again, I think it is a must have mod - as Michael said, 100% noticeable gains. Definite increased response but the biggest benefit I think is the increased low down response. Turbo spools earlier and quicker and in 2nd and 3rd gear accelerating to 100km on the freeway you really do feel that extra kick. I have aftermarket axle back exhausts, but I did not notice a significant amount of cabin noise cruising or just driving around town... will test this theory out with the missus when she drives it. Give it a bit though, and the note does sound more aggressive... I have previously missed the rumble of the WRX, but I'm really beginning to like the sound of the twin scroll/2L GT. There is increased intake noise (HKS panel filter) - if I do the resonator delete I think that would be enough noise for me... I did own the SPT intake prior to this but prefer the lower note of the exhausts over the noise of the intake. Will attempt another video and compare to the old one over the weekend.
Thanks to Michael/PhatGT. Perfect fit. Heat shield trimming pictures spot on. Russell from Subievolution here in QLD was impressed with the fitment (he's had many issues with customers bringing in exhaust systems before which simply do not bolt on).
Also had lower control arm bushes installed (Phat/J speed ones). Old ones (60,000km old) were basically cracked... I think they were causing my occasional shudder in the steering wheel because that stopped happening on the freeway today. Will test it out a bit more before I explore rotor options. Wheel alignment this afternoon and I am one very happy owner.
These two mods and the short shifter are fantastic bang for buck mods.
Unfortunately, left rocker gasket cover leaking so will have to get that fixed first before I explore sway bars/brakes/centre pipe/TMIC as next upgrades. And please someone buy that BOV from Leo before I get tempted.
What I did discover is ... find a good mechanic and go back to them. The last couple of services I took it to a dealership and they did look after me when my clutch died and I needed a tow (were the only place open) and I was grateful for that. However, when installing the dump pipe today, their workmanship was questionable. The stock dump (which we presume was removed at time of clutch install) had 3 bolts not adequately done up and there had been some leaking around it... so I've told the missus that the stock pipe was leaky and that was why I needed a new one!

No long term harm done though I think.
Apologies for the long post, but extremely happy with both mods today
Photo of stock dump pipe with burn marks and another photo of Phat's handiwork.