Bill, your maths are absolutely correct, but I don't think it will make such a huge difference in top gear performance.
According to my self-made gear-ratio - speed - rpm Excel spreadsheet, the standard gearing (21T-43T-19T-42T) would result in 4050 rpm @ 60mph in 4th gear (4900 in 3rd). Hubies 22T engine sprocket will result in 3860 at the same speed (4680 in 3rd). You might have to stay in third a bit longer, but still it should be pulling well enough in 4th I would think.
All values assuming a STD clutch basket and g'box sprocket is fitted.