shure about that 3.92?
the 230.6 i have had that ratio thou, and i am from Europe, so might be different.

either way, how far of is your current speedometer? is it spot on, or shows a tad to much (as al of mine has) it might be that your current speedometer will show a more correct speed with a 3.69 than the current 3.92.

the 220d isnt fast, but it can handle a 3.69differential without much problems, giving you a nicer less screamy ride RPM wise. aswell as a tad better MPG.

you could always get the speedo from the 230.4 at the junkyard "worst" case scenario.

/me that has that mbturbo.com site.