An AU2 XR8 is already rated at 200kw, so it depends on what else you've done. I've just put a 70mm TB on my AU2 V8 (non-XR), which has K&N air filter, rebored MAF sensor tube, pacemakers, high flow cats (6 litres per side) and full 3" system with straight through muffler. I did the TB before the 3" and noticed some better throttle response, but not much else. Since the 3" system, I've noticed heaps better pull right through the rev range, but especially from 1000 - 2000rpm, and again between 4000-5500 rpm.
The Tickford ones are not as expensive as they once were. Herrod Motorsport now sells them for $550 plus GST + postage. You can order them from Rob direct ph 03 9464 5100.
Rob did tell me that I would need their ceramic intake tube (from MAF to TB), but I have not found that to be the case.
Give Rob a call - he's a wealth of knowledge, and will tell you the benefits etc of whatever mod you do.
AU1 XR8 Auto 147.9 rwkw (approx 215 fwkw)
AU2 Wagon HAD Auto
17s, Pacemakers, 3" Intake & Pod filter (The Family Hack)
FPV-XR Club ACT