I put a post up a long time ago regarding the 2.56 and 3..31 gears in the SS cars. I have yet to find a 70 SS that had anything other than a 2.56......same goes for the 3.31 in 71. I'm not saying they didn't exist, but I haven't seen otherwise. Oddly, the Canadian version of the sales brochure lists 3.31 as the only gear for the 70 SS454, yet all I've seen is 2.56 for 70.,
Anyway, I agree with the others that 3.31 is a great all around gear. With 3.31s, I have found that you can really tweak your highway cruising rpm with tire size. With a shorter tire, I find myself in the slow lane doing 3000 rpms at about 65, but now I'm running the tall 28" tires (275/60/15), and I cruise at under 3k at 70....in the middle lane!
If you are building a low to mid range 454, I think the 3.08 would be the best all around gear for both city and highway....maybe with mild converter.
Dennis - those mph/rpm calculations include torque converter loss? With my mild converter, I take my foot off the gas on the highway and the rpms immediately drop like 400 or 500 rpms.