I was having the same decision making trouble and made some rpm calculations for the ERA 3.54 and 3.31 rear ends. See pages 2 and 3 of this thread:
ERA #783 - with questions
I've decided to go with the 3.31 rear and the 0.82 5th for the better shift and balance, and I'll deal with the higher rpms and noise at higher speeds - which can be frequent on Florida freeways.
I'll let you know how it turns out.
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Mooch
ERA Registry Map
If you have an ERA and want to be listed, contact me with your info and I'll put it up. The minimum info I need is chassis number and location. The rest is up to you. The most information needed would be: chassis number, body type, city, name, CC nickname, and email address.