JP...if you will go to out website
www.427cobras.com and select "contact us"...go ahead, dont be bashful, you will receive an Ebrochure. Then select the "gearbox" option. Viola! There is a table for a 351 Windsor 385 H.P., TREMEC 3550 series, with a 3.50 / 3.73 / 4.10 ratio. Should empirically show you abour everything you want to know. Personally speaking I like the 3.50. Couple of days ago we were putting a new car through its pre-delivery shakedown. I wans't paying attention ( can't believe that I admitted that ) and came off a light in 4th. Just hit the clutch friction point, bring it up to 1000 rpm from 775 idle, and motor on off down the street. It's quite surprising that you could drive the car in one gear ( ALTHOUGH WE EMPHATICALLY DONT RECOMEND IT ). 2380 lbs isnt hard to move with 400+ ft/lbs of torque. If you choose to NAIL it, it's a WHITE KNUCKLE RIDE in any gear. Be careful out there!
For "normal" street driving, higher ratios just tend to jack the RPMs up which burns gas and wears engines. We dont supply less than the 3.50 and caution against anything higher than 3.73.
So! There's our penny's worth. All the best and enjoy your ride!!