The Toyota 1UZ-FE engine in the Lexus is a brilliant engine. It obviously has one-arm tied behind it's back with the Auto 'box (and a lot of weight). I still agree it's impressive the JTD is faster! While giving better economy too!
I was driving the JTD 20v I now own (wasn't mine at the time) - had been in the company of the owner of a modified Nissan Skyline R33 GTS-T (2.5 litre 24v straight-six single turbo, rwd). It was running water/methanol injection and a claimed ~350bhp. We joined the motorway together side by side, both floored it. I was amazed that we pulled away from him slightly!
It's the reason I recently got a train half way across the country to buy it!
Stumbled across by accident a couple of years after my friend sold it. I've driven lots of diesel cars from modern Lexus, Insignia, E39 BMW to Old school Xantia. None had the combination of performance and fuel economy this remapped 20v has. I always mention the remap however, as like any turbo car I think the increased boost pressure makes all the difference to torque output. It's a bonus that diesel maps give even better economy too!
No doubt a GTA driver will rubbish the claims or say "yeah, it's too heavy at the front to corner though" but that's down to the driver. I've just swapped from an E39 540i (4.4 V8) with a Steptronic 'box and Sport suspension and I would say the 20v performance is comparable to that when in 'Sport' mode, which is saying something.
Only downside to the 20v as far as I can tell is the reliability, cost of components and the facelift rear lights (personal taste). So it's not perfect, but definitely goes very well and sounds good too.