Going back very briefly to when I asked about how gear ratios work, I asked a mate who explained that you simply multiply the given gear ratio by the final drive ratio. Using the two examples I gave, and just to show what difference the FD can make on a car, here's a couple of graphs I knocked up:
Top one is original ratios, bottom one is multiplied by the final drive. Given the Zed has a marginally shallower curve, I'd say that it's probably got a closer 'box than the 911 does. However, you can now see why the 911 feels so much quicker than a 350 (and why the FI Zeds feel bonkers) as you've got a load more power but an almost identical curve. Of course, we're now miles off tangent but I thought it would be interesting to view the comparison.
For sh*ts and giggles, here's the chart comparing the two cars above with a host of options that the Cobra kitcar builders have. The T56 is the spec my mate is using on a 427 block, the other specs are the gearings used on the original Cobras, in both close ratio and wide ratio options in two different FDs: