2 questions ?
As far as punch from a roll, it depends what gear you kick down into. I don't know the specs off hand, but 2.73s are a TALL *** gear...you'll have much better results with a 3.42, in almost any situation.
Converter is nice if you like racing. I don't like converters. Too much of a loose feeling, and say goodbye to your gas mileage. I like the stock powerband, which you will lose with a conveter. But...they are faster if you are racing...
Go to my web page and go to the gear ratios page. I have a link to a spreadsheet entitled "ratios.xls". You can plug in your AUTO ratios, and rear end ratios, and play with the mphs. That's what I did to create the gear ratios page I have on my web page, but that page is for M6 only...

