Check out this page for tons of automotive calculators
http://www.cobranet.com/calcs.htm
Check out the gearing calculator.
My SPF has 3.73 rear gears with the 3.27 first gear in Tremec 5 sp. The motor is a mild Oltoff 357W making 415 HP and will idle at 600 RPM. If I mash the pedal, sometimes it will go straight with lots of rubber. But sometimes it wants to swap ends.
Bought it used from original owner. I agree about the first gear being too much for general cruisin. When I slow down for something and I'm still rolling, I usually just shift into second and take off. I only put it in first when I'm stopped and want to make more noise, or accelerate to the speed limit in a more rapid manner
I have the 8.8 diff, and no problems in 6K miles. The new diff is supposed to be better, but what do I know ... I'm a newbie ... only had it for a year. I get so many questions about the car, I wrote up a "Car Show Handout". I keep a bunch in the trunk and use it as a memory check, or give them a copy if they ask for it. I've posted it in my pictures section.
There are a ton of other posts regarding gearing on CC. You might want to do a search.