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We have a 31 Tudor with a strong engine, Mitchell overdrive 26% and Mitchell gearbox with 15% higher 1st and second. Diff is 3.78 and tyres are 16 inch on V8 rims.
This is a nice car to drive, but every now and then on really steep 180 degree uphill bends needs first gear to avoid straining. On the other hand on long uphill pulls in the hills where top gear is too high, overdrive second really speeds things up.
Our Roadster with a very strong engine cannot go as fast up these hills where second gear is needed without going over my 2600 rev limit. But it pulls the very tight uphill bends in second gear ok. It has 19 inch wheels with Excelsior sport radials 155X19. Gearbox is standard Model A, overdrive is 26% Mitchell and rear end 3.78.
Both are a delight to drive and impossible to say which is best.
Reading this to myself I think the message is stay with 3.78, put in 26% Mitchell o/d and if your gearbox needs any kind of attention put in the Mitchell synchro internals. For a strong engine ( higher compression, better camshaft, larger carb.) go for higher first and second gear ratios. For a standard engine I am not sure on this last point. One can up the ratio on either or none of first and second gears.
I put a plus 15% first and second in a friends cabriolet with standard diff and tyres. His only comment is "it goes very fast in reverse now, especially in backing out of my shed". He is 85 and a rather slow driver.
SAJ in NZ