I modded an Auto R31 Ghostrider. After the Turbo went in, the stock auto lasted about 2 seconds. (Slight exageration there). And I decided to keep the car auto, rather than go the manual conversion. With an Auto, they stay on boost and have less lag. Brescani racing have their cars as auto as well, and I would assume its for the same reason.
Wouldn't bother putting a shift kit in one though. Waste of money if you are going to do nothing else. A manual conversion is always another option, if you can't afford to do an auto properly, but its always good to know what you are doing with a manual conversion as well. I have seen some shockers.
Yarra Valley Automatics rebuilt my series 3 auto to handle 300 KW, and it does a fine job with 225 KW, (flywheel). BUT, I have a manual car as well, so I can still get my manual fix.