If you had 2 converters with the same stall but one was a 10" and one was a 12", how would they differ in performance?. I realize the 10" would tend to run hotter due to less fluid but wanted to know why they are built to different diameters.

it depends on the stall speed. A 10" converter with a 1200 rpm stall speed, would not likely work as good as a 12",

A 10" would definately be more effiecient in the 3000 rpm stall range than a 12" built to stall that high.

You are inherently building a less efficient converter by changing fin angle, windowing the stator, or different stator fin configuration.
However all things being equal a smaller converter stalls higher.

So a smaller converter with a more ideal fin angle and stator configuration will be much more efficient than a larger converter with "sloppier" configuration.

Thanks for the explanation jakeshoe!. I guess it depends on the quality. I have seen board members recommend these 3 companies. These are the models I think would be good for me. Roadrunner:http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=7997478697&ssPageName=STRK:MEWA:IT
Redneck:http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=7998395468&ssPageName=STRK:MEWA:IT
Transmission Specialties:http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=7993794802&ssPageName=STRK:MEWA:IT

Redneck has a 10" but the other two are 12". All have similar stalls (2200-2800 range) and all 3 companies tech support people said their model was perfect for my combo. Redneck seems like pretty decent components but I just want to make sure I get the right one. Do these look like good choices for my combo?

Of the three I posted, does the 10" look like the best pick?