The larger rotating mass of a stock 12 inch D5 converter will help keep the engine spinning if you suddenly let of the gas such as right after doing a burnout when the idle can suddenly drop to below before the IAC motor can recover. Sometimes with smaller converters that dont have the large rotating mass of a stock converter the engine can stall and die before the IAC can catch up. A modified chip accounts for the reduced rotating mass. I have seen numerous Buicks stall at the track right after doing a burnout when they let off the gas.
As for driving impressions...well..the engine revs quicker, the turbo spools like lightning with a stock turbo...it made my PT52 behave almost like a stock turbo and converter combo...and with a ball bearing turbo it will spool like a supercharged car. Watch driving on wet roads because it can make your tires blow off VERY quickly. Just normal driving around...slightly higher RPM's until the converter locks at which point its just like driving a stocker. Its one of the best mods I've done yet to my car. I love it. The muti-disc units do chatter a bit...but thats normal. I only have a single disc but it works just fine.