The only difference between the two TKO 600's is just the overdrive ratio. I sell a lot of the .82 ratios because most of my customers either have high rearend ratios, or fussy engines.
Ernie, that disc is actually a sintered iron/sintered iron disc. It is in fact very aggressive....but rated for 650hp, which is what was needed to support a big FE and a set of slicks.
The smaller 11" clutch size helps keep the chatter down, plus a 2500 lb car doesn't hurt either.